Add clang-tidy external examples

clang-tools-extra/docs/clang-tidy/ExternalClang-TidyExamples.rst

@@ -0,0 +1,32 @@
+=======================
+External Clang-Tidy Examples
+=======================
+
+Introduction
+============
+
+This page provides examples of what people have done with `clang-tidy`` that 
+might serve as useful guides (or starting points) to develop your own checks. 
+They may be helpful for necessary things such as how to write CMakeLists.txt 
+for an out-of-tree plugin of `clang-tidy` checks.
+
+If you know of (or wrote!) a tool or project using clang-tidy, please share it 
+on `the Discourse forums (Clang Frontend category)
+<https://discourse.llvm.org/c/clang/6>`_ for wider visibility and open a 
+pull-request on `LLVM Github`_ to have it added here. Since the primary purpose of 
+this page is to provide examples that can help developers, generally they must have 
+code available.
+
+As `clang-tidy` shares C++ AST Matchers with Clang diagnostics, `External Clang Examples`_ 
+may also be useful to look at for examples.
+
+.. _LLVM Github: https://github.com/llvm/llvm-project
+.. _External Clang Examples: https://clang.llvm.org/docs/ExternalClangExamples.html
+
+https://clang.llvm.org/docs/ExternalClangExamples.html
+
+List of projects and tools
+==========================
+
+`<https://github.com/coveooss/clang-tidy-plugin-examples/tree/main>`_
+    "This folder contains clang-tidy plugins."