cvsps: update docstring for changeset class.

hgext/convert/cvsps.py

@@ -428,6 +428,7 b' def createlog(ui, directory=None, root="'
 
 class changeset(object):
     '''Class changeset has the following attributes:
+        .id        - integer identifying this changeset (list index)
         .author    - author name as CVS knows it
         .branch    - name of branch this changeset is on, or None
         .comment   - commit message