add a note about CLANG_TIDY_IGNORE_SOURCES to docs (#2789)

Co-authored-by: Eric T. Johnson <[email protected]>

Docs/source/debugging.rst

@@ -85,6 +85,12 @@ You can also use ask it to fix errors automatically via:
 
 and you can treat warnings as errors by adding ``CLANG_TIDY_WARN_ERROR=TRUE``.
 
+.. note::
+
+   Building a Castro problem with ``clang-tidy`` will suppress the
+   checks in AMReX and Microphysics sources and headers.  This is set by
+   the parameter ``CLANG_TIDY_IGNORE_SOURCES`` in ``Make.Castro``, and
+   the ``HeaderFilterRegex`` whitelist in ``.clang-tidy``.
 
 
 Thread sanitizer
@@ -121,5 +127,3 @@ to operate over.
 
 Physics issues
 ==============
-
-