[analyzer][docs] Fix the incorrect structure of the checker docs

[Szelethus]

Summary

The alpha.security.cert section came right after alpha.security, making it look like checkers like alpha.security.MmapWriteExec belonged to that package.

[steakhal]

Hmm, something is still bad.

[Szelethus]

Fix incorrect sectioning.

[Szelethus]

Add context.

[steakhal]

Looks great. Thanks.

clang/docs/analyzer/checkers.rst

reminderText =
      [NSString stringWithFormat:
        NSLocalizedString(@"%@ Reminders", @"Indicates multiple reminders"),
          reminderCount];
  }
 
 alpha.security
 ^^^^^^^^^^^^^^
 
-
-alpha.security.cert
-^^^^^^^^^^^^^^^^^^^
-
-SEI CERT checkers which tries to find errors based on their `C coding rules <https://wiki.sei.cmu.edu/confluence/display/c/2+Rules>`_.
-
-.. _alpha-security-cert-pos-checkers:
-
-alpha.security.cert.pos
-^^^^^^^^^^^^^^^^^^^^^^^
-
-SEI CERT checkers of `POSIX C coding rules <https://wiki.sei.cmu.edu/confluence/pages/viewpage.action?pageId=87152405>`__.
-
-.. _alpha-security-cert-pos-34c:
-
-alpha.security.cert.pos.34c
-"""""""""""""""""""""""""""
-Finds calls to the ``putenv`` function which pass a pointer to an automatic variable as the argument.
-
-.. code-block:: c
-
-  int func(const char *var) {
-    char env[1024];
-    int retval = snprintf(env, sizeof(env),"TEST=%s", var);
-    if (retval < 0 || (size_t)retval >= sizeof(env)) {
-        /* Handle error */
-    }
-
-    return putenv(env); // putenv function should not be called with auto variables
-  }
-
-alpha.security.cert.env
-^^^^^^^^^^^^^^^^^^^^^^^
-
-SEI CERT checkers of `POSIX C coding rules <https://wiki.sei.cmu.edu/confluence/x/JdcxBQ>`__.
-
-.. _alpha-security-cert-env-InvalidPtr:
-
-alpha.security.cert.env.InvalidPtr
-""""""""""""""""""""""""""""""""""
-
-Corresponds to SEI CERT Rules ENV31-C and ENV34-C.
-
-ENV31-C:
-Rule is about the possible problem with `main` function's third argument, environment pointer,
-"envp". When enviornment array is modified using some modification function
-such as putenv, setenv or others, It may happen that memory is reallocated,
-however "envp" is not updated to reflect the changes and points to old memory
-region.
-
-ENV34-C:
-Some functions return a pointer to a statically allocated buffer.
-Consequently, subsequent call of these functions will invalidate previous
-pointer. These functions include: getenv, localeconv, asctime, setlocale, strerror
-
-.. code-block:: c
-
-  int main(int argc, const char *argv[], const char *envp[]) {
-    if (setenv("MY_NEW_VAR", "new_value", 1) != 0) {
-      // setenv call may invalidate 'envp'
-      /* Handle error */
-    }
-    if (envp != NULL) {
-      for (size_t i = 0; envp[i] != NULL; ++i) {
-        puts(envp[i]);
-        // envp may no longer point to the current environment
-        // this program has unanticipated behavior, since envp
-        // does not reflect changes made by setenv function.
-      }
-    }
-    return 0;
-  }
-
-  void previous_call_invalidation() {
-    char *p, *pp;
-
-    p = getenv("VAR");
-    pp = getenv("VAR2");
-    // subsequent call to 'getenv' invalidated previous one
-
-    *p;
-    // dereferencing invalid pointer
-  }
-
 .. _alpha-security-ArrayBound:
 
 alpha.security.ArrayBound (C)
 """""""""""""""""""""""""""""
 Warn about buffer overflows (older checker).
 
 .. code-block:: c
 
int *test() {
    return p; // warn
  }
 
  int test(void) {
    int x;
    return x; // warn: undefined or garbage returned
  }
 
+
+alpha.security.cert
+^^^^^^^^^^^^^^^^^^^
+
+SEI CERT checkers which tries to find errors based on their `C coding rules <https://wiki.sei.cmu.edu/confluence/display/c/2+Rules>`_.
+
+.. _alpha-security-cert-pos-checkers:
+
+alpha.security.cert.pos
+^^^^^^^^^^^^^^^^^^^^^^^
+
+SEI CERT checkers of `POSIX C coding rules <https://wiki.sei.cmu.edu/confluence/pages/viewpage.action?pageId=87152405>`_.
+
+.. _alpha-security-cert-pos-34c:
+
+alpha.security.cert.pos.34c
+"""""""""""""""""""""""""""
+Finds calls to the ``putenv`` function which pass a pointer to an automatic variable as the argument.
+
+.. code-block:: c
+
+  int func(const char *var) {
+    char env[1024];
+    int retval = snprintf(env, sizeof(env),"TEST=%s", var);
+    if (retval < 0 || (size_t)retval >= sizeof(env)) {
+        /* Handle error */
+    }
+
+    return putenv(env); // putenv function should not be called with auto variables
+  }
+
+alpha.security.cert.env
+^^^^^^^^^^^^^^^^^^^^^^^
+
+SEI CERT checkers of `Environment C coding rules <https://wiki.sei.cmu.edu/confluence/x/JdcxBQ>`_.
+
+.. _alpha-security-cert-env-InvalidPtr:
+
+alpha.security.cert.env.InvalidPtr
+""""""""""""""""""""""""""""""""""
+
+Corresponds to SEI CERT Rules ENV31-C and ENV34-C.
+
+ENV31-C:
+Rule is about the possible problem with `main` function's third argument, environment pointer,
+"envp". When enviornment array is modified using some modification function
+such as putenv, setenv or others, It may happen that memory is reallocated,
+however "envp" is not updated to reflect the changes and points to old memory
+region.
+
+ENV34-C:
+Some functions return a pointer to a statically allocated buffer.
+Consequently, subsequent call of these functions will invalidate previous
+pointer. These functions include: getenv, localeconv, asctime, setlocale, strerror
+
+.. code-block:: c
+
+  int main(int argc, const char *argv[], const char *envp[]) {
+    if (setenv("MY_NEW_VAR", "new_value", 1) != 0) {
+      // setenv call may invalidate 'envp'
+      /* Handle error */
+    }
+    if (envp != NULL) {
+      for (size_t i = 0; envp[i] != NULL; ++i) {
+        puts(envp[i]);
+        // envp may no longer point to the current environment
+        // this program has unanticipated behavior, since envp
+        // does not reflect changes made by setenv function.
+      }
+    }
+    return 0;
+  }
+
+  void previous_call_invalidation() {
+    char *p, *pp;
+
+    p = getenv("VAR");
+    pp = getenv("VAR2");
+    // subsequent call to 'getenv' invalidated previous one
+
+    *p;
+    // dereferencing invalid pointer
+  }
+
+alpha.security.taint
+^^^^^^^^^^^^^^^^^^^^
+
+Checkers implementing `taint analysis <https://en.wikipedia.org/wiki/Taint_checking>`_.
+
 .. _alpha-security-taint-TaintPropagation:
 
 alpha.security.taint.TaintPropagation (C, C++)
 """"""""""""""""""""""""""""""""""""""""""""""
 Generate taint information used by other checkers.
 A data is tainted when it comes from an unreliable source.
 
 .. code-block:: c