add a few more docs to existing funcs

Change-Id: I27317a59aba67c05ca1fd333e8f064c0edccb209
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/343185
Reviewed-by: LaMont Jones <lamontjones@google.com>
Tested-by: Mike Frysinger <vapier@google.com>
diff --git a/git_command.py b/git_command.py
index 5d73c28..a176927 100644
--- a/git_command.py
+++ b/git_command.py
@@ -158,6 +158,8 @@
 
 
 class GitCommand(object):
+  """Wrapper around a single git invocation."""
+
   def __init__(self,
                project,
                cmdv,