Bug 1812046 - add missing ac_add_options directive to debugging macos docs; r=haik

Differential Revision: https://phabricator.services.mozilla.com/D167663

docs/contributing/debugging/debugging_on_macos.rst

@@ -15,14 +15,14 @@ this in your .mozconfig
 
 .. code::
 
-   --disable-optimize
-   --enable-debug-symbols
+   ac_add_options --disable-optimize
+   ac_add_options --enable-debug-symbols
 
 you can also add this flag if you want assertions etc. compiled in
 
 .. code::
 
-   --enable-debug
+   ac_add_options --enable-debug
 
 See :ref:`Building Firefox for macOS <Building Firefox On MacOS>`
 if you need help creating your own build.