[clang-tools-extra] Update clang tidy Contributing guide (PR #106672)

[Julian Schmidt via cfe-commits]

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@@ -690,8 +716,8 @@ warnings and errors. The script provides multiple configuration flags.
   that the file names are matched against.
   ``run-clang-tidy.py clang-tidy/.*Check\.cpp`` will only analyze clang-tidy
   checks. It may also be necessary to restrict the header files that warnings
-  are displayed from using the ``-header-filter`` flag. It has the same behavior
-  as the corresponding :program:`clang-tidy` flag.
+  are displayed from using the ``-exclude-header-filter`` flag. It has the same 
+  behavior as the corresponding :program:`clang-tidy` flag.
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5chmidti wrote:

A restriction on which header files to present diagnostics from can be an inclusion or exclusion restriction, so we probably want to mention both flags here.

https://github.com/llvm/llvm-project/pull/106672