Merge ~adam-collard/gitlptools:usage-doc into ~ubuntuone-hackers/gitlptools:master

[Adam Collard]

Add usage docs

diff --git a/src/gitlptools/__init__.py b/src/gitlptools/__init__.py
index f9c36d4..f72dae9 100644
--- a/src/gitlptools/__init__.py
+++ b/src/gitlptools/__init__.py
@@ -132,7 +132,7 @@ def get_launchpad_branch(lp, repo):
 
 def git_lp_approve(argv=sys.argv[1:]):
     """Approve the MP on LP linked to this git branch."""
-    parser = argparse.ArgumentParser()
+    parser = argparse.ArgumentParser(usage=git_lp_approve.__doc__)
     parser.add_argument(
         "--dry-run", action="store_true", default=False,
         help="Dry run - Don't actually approve the MP.")
@@ -177,7 +177,7 @@ def git_lp_approve(argv=sys.argv[1:]):
 
 def git_lp_open(argv=sys.argv[1:]):
     """Open LP page for current git branch."""
-    parser = argparse.ArgumentParser()
+    parser = argparse.ArgumentParser(usage=git_lp_open.__doc__)
     parse_args_with_logging(parser, argv)
     repo = _get_this_repo()
     if len(repo.remotes) == 0:
@@ -193,7 +193,7 @@ def git_lp_open(argv=sys.argv[1:]):
 
 def git_lp_propose(argv=sys.argv[1:]):
     """Propose MP for the current git branch."""
-    parser = argparse.ArgumentParser()
+    parser = argparse.ArgumentParser(usage=git_lp_propose.__doc__)
     parser.add_argument(
         'merge_target', nargs='?', action=MergeTargetAction,
         help=(