[recipes.py] add missing helpstrings, merge test subcommands into main parser.

recipe_engine/doc.py

Index: recipe_engine/doc.py
diff --git a/recipe_engine/doc.py b/recipe_engine/doc.py
index eeeeec31f77738409e4d91de4defb2c8936a60b0..ba4d606e1ad2ec1788fd2dfd866af62c2613fe3c 100755
--- a/recipe_engine/doc.py
+++ b/recipe_engine/doc.py
@@ -460,10 +460,12 @@ def _set_known_objects(base):
 def add_subparser(parser):
   doc_kinds=('binarypb', 'jsonpb', 'textpb', 'markdown(github)',
              'markdown(gitiles)')
+  helpstr = (
+    'List all known modules reachable from the current package, with their '
+    'documentation.'
+  )
   doc_p = parser.add_parser(
-      'doc',
-      description='List all known modules reachable from the current package, '
-          'with their documentation')
+    'doc', help=helpstr, description=helpstr)
   doc_p.add_argument('recipe', nargs='?',
                      help='Restrict documentation to this recipe')
   doc_p.add_argument('--kind', default='jsonpb', choices=doc_kinds,