[clang] [clang][docs] Add all clang-tools-extra (PR #148622)

[via cfe-commits]

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@@ -89,14 +89,53 @@ they'll be tracked here. The focus of this documentation is on the scope
 and features of the tools for other tool developers; each tool should
 provide its own user-focused documentation.
 
-``clang-tidy``
+``Clang-Doc``
+-------------
+
+`clang-doc <https://clang.llvm.org/extra/clang-doc.html>`_ is a tool for
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weirdsmiley wrote:

I was following similar syntax to their internal docs. For e.g., in this [page](https://clang.llvm.org/extra/clang-tidy/), the title (`Clang-Tidy`) has first letters capitalized, but inside the paragraph the tool is referenced with all small letters (`clang-tidy`).

I can change it here if that makes more sense.

https://github.com/llvm/llvm-project/pull/148622