[clang-tidy] Add missing IgnoreMacros doc for modernize-use-equals-default.

A followup of rL311136.

llvm-svn: 311654
GitOrigin-RevId: e928c2b67e1a6946faa5c601fc3616701193bb82

docs/clang-tidy/checks/modernize-use-equals-default.rst

diff --git a/docs/clang-tidy/checks/modernize-use-equals-default.rst b/docs/clang-tidy/checks/modernize-use-equals-default.rst
index b87f883..4b2368c 100644
--- a/docs/clang-tidy/checks/modernize-use-equals-default.rst
+++ b/docs/clang-tidy/checks/modernize-use-equals-default.rst
@@ -26,3 +26,11 @@
 
 .. note::
   Move-constructor and move-assignment operator are not supported yet.
+
+Options
+-------
+
+.. option:: IgnoreMacros
+
+   If set to non-zero, the check will not give warnings inside macros. Default
+   is `1`.