Help: Trivial typo fix for CMAKE_XCODE_GENERATE_SCHEME

Help/variable/CMAKE_XCODE_GENERATE_SCHEME.rst

 CMAKE_XCODE_GENERATE_SCHEME
 ---------------------------
 
-If enabled, the Xcode generator will generate schema files. Those are
+If enabled, the Xcode generator will generate schema files.  These
 are useful to invoke analyze, archive, build-for-testing and test
 actions from the command line.