plonecli usage enhancement

[ksuess]

% plonecli
respond with help text, same as "plonecli --help"

% plonecli -l
respond with:
You can create an add-on with "plonecli addon"
You can add the following features to your add-on with "plonecli add feature_name". Change to add-on directory before.
- behavior
- content_type
- controlpanel
- etc

% plonecli add -h
It would be handsome to see a list what I can add.
Suggestion: Respond with list of features that can be added to my Plone add-on.

plonecli -V
plonecli : 2.2
bobtemplates.plone: 6.0b12