Explain get_new_commits behaviour at pre-receive hook

Author: kofrezo

igcommit/git.py

@@ -50,6 +50,10 @@ def __eq__(self, other):
 
 defget_new_commits(self):
 """Get the list of parent new commits in order"""
+
+# At pre-receive hook we get one id for each branch pushed and need to
+# find commits to be tested. With the test command from the README.md
+# this returns nothing.
 output=check_output([
 git_exe_path,
 'rev-list',