[clangd] Make -clang-tidy-checks a non-hidden command-line arg

[ilya-biryukov]

Summary

This looks like a useful user-facing configuration parameter,
which should be discoverable.

Also fix a small typo in the description.

clang-tools-extra/trunk/clangd/tool/ClangdMain.cpp

static llvm::cl::opt<bool> EnableFunctionArgSnippets(
     "function-arg-placeholders",
     llvm::cl::desc("When disabled, completions contain only parentheses for "
                    "function calls. When enabled, completions also contain "
                    "placeholders for method parameters."),
     llvm::cl::init(CodeCompleteOptions().EnableFunctionArgSnippets));
 
 static llvm::cl::opt<std::string> ClangTidyChecks(
     "clang-tidy-checks",
-    llvm::cl::desc("List of clang-tidy checks to run (this will overrides "
+    llvm::cl::desc("List of clang-tidy checks to run (this will override "
                    ".clang-tidy files)"),
-    llvm::cl::init(""), llvm::cl::Hidden);
+    llvm::cl::init(""));
 
 static llvm::cl::opt<bool> SuggestMissingIncludes(
     "suggest-missing-includes",
     llvm::cl::desc("Attempts to fix diagnostic errors caused by missing "
                    "includes using index."),
     llvm::cl::init(false));
 
 namespace {