clarify source control point

Basic/Pod/PP.pod

@@ -543,14 +543,15 @@ error what is wrong with your args to C<pp_def>). Although work is being
 done to produce better warnings, do not be afraid to send your questions to
 the mailing list if you run into trouble.
 
-Another problem arises from the number of generated files that may be
+There are a number of generated files that may be
 confusing, especially when dealing with existing code.
 Bear in mind that the only sources are C<.pd> and C<.pod> files, while
 C<.pm>, C<.xs> and C<.c> files are generated from the C<.pd> files and
-shall not be altered as these changes would be overwritten.
+should not be altered manually as these changes would be overwritten - modify
+the C<.pd> file instead.
 
-Furthermore, the generated files shall neither be part of a distribution nor
-under version control and therefore
+Furthermore, since the generated files should not be part of a distribution nor
+under version control, they
 should be listed in C<MANIFEST.SKIP> and e.g. C<.gitignore>.
 
 =head1 DESCRIPTION