- add some rules with explanation

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@37994 20353a03-c40f-0410-a6d1-a30d3c3de9de

buildout/hooks/README.txt

+It is disallowed to:
+
+ * use hooks directory directly in buildout (eg. assuming that it will exists
+   while running buildout)
+
+Rationale: It disallows using buildout in networked environment and extending
+           over network.
+
+ * accesing hooks by SVN URI
+
+Rationale: It forces to use SVN structure and makes mirroring and HA hard to
+           obtain.