update readme for new purpose of repo

Author: eteq

README.md

@@ -1,2 +1,5 @@
-# community-engagement
-Documents and policies regarding community engagement and management.
+# Astropy Project-wide repository
+
+Documents and policies regarding the Astropy Project as a whole.  *Drafts* of policies under consideration go into the `drafts` directory.  Other directories can be created as needed to maintain organization, but as a general guideline a new directory should not be created unless it contains (or will contain) at least 3 files.
+
+Additionally, the issue tracker will be used to discuss larger Project-wide issues. (I.e., those that are not particular to a specific pacakge or other repository.)