[clang-tidy] Fix bugprone-copy-constructor-init documentation

[PiotrZSL]

Summary

Correct example, and add information about limitations.

Fixes: https://github.com/llvm/llvm-project/issues/55572

[Eugene.Zelenko]

clang-tools-extra/docs/clang-tidy/checks/bugprone/copy-constructor-init.rst

37

English is not my native tongue, but may be the check is correct?

[PiotrZSL]

Update doc

[PiotrZSL]

Update doc

[carlosgalvezp]

Great improvement, thanks!

clang-tools-extra/docs/clang-tidy/checks/bugprone/copy-constructor-init.rst

 .. title:: clang-tidy - bugprone-copy-constructor-init
 
 bugprone-copy-constructor-init
 ==============================
 
-Finds copy constructors where the constructor doesn't call
-the copy constructor of the base class.
+Finds copy constructors where the constructor doesn't call the copy constructor
+of the base class.
 
 .. code-block:: c++
 
     class Copyable {
     public:
       Copyable() = default;
       Copyable(const Copyable &) = default;
+
+      int memberToBeCopied = 0;
     };
+
     class X2 : public Copyable {
       X2(const X2 &other) {} // Copyable(other) is missing
     };
 
 Also finds copy constructors where the constructor of
 the base class don't have parameter.
 
 .. code-block:: c++
 
-    class X4 : public Copyable {
-      X4(const X4 &other) : Copyable() {} // other is missing
+    class X3 : public Copyable {
+      X3(const X3 &other) : Copyable() {} // other is missing
     };
 
+Failure to properly initialize base class sub-objects during copy construction
+can result in undefined behavior, crashes, data corruption, or other unexpected
+outcomes. The check ensures that the copy constructor of a derived class
+properly calls or initializes the copy constructor of the base class, which
+helps prevent bugs and improves code quality.
+
+Limitations:
+
+* It won't generate warnings for empty classes, as there are no class members
+  (including base class sub-objects) to worry about.
+
+* It won't generate warnings for base classes that have copy constructor
+  private or deleted.
+
+* It won't generate warnings for base classes that are initialized using other
+  non-default constructor, as this could be intentional.
+
 The check also suggests a fix-its in some cases.