Move Nathan to the inactive maintainers section

Based on review feedback from Nathan -- thank you for all the help!

Author: AaronBallman

clang-tools-extra/Maintainers.txt

@@ -30,13 +30,18 @@ clang-doc
 | [email protected] (email)
 
 
-clang-tidy
-----------
-| Nathan James
-| [email protected] (email), njames93 (GitHub)
-
-
 clangd
 ------
 | Sam McCall
 | [email protected] (email), sam-mccall (GitHub), sam-mccall (Discourse), sam-mccall (Discord)
+
+
+Inactive Maintainers
+====================
+The following people have graciously spent time performing maintainership
+responsibilities but are no longer active in that role. Thank you for all your
+help with the success of the project!
+
+Inactive component maintainers
+------------------------------
+| Nathan James ([email protected]) -- clang-tidy