every command needs to respond to --help and --description

[marcoceppi]

Currently, we're failing at being good charm tools because of the following:

marco@T430:~$ charm help plugins
ERROR 'charm-create --description': exit status 2
ERROR 'charm-add --description': exit status 2
ERROR 'charm-proof --description': exit status 2
ERROR 'charm-build --description': exit status 2
ERROR 'charm-layers --description': exit status 2
charm plugins

Plugins are implemented as stand-alone executable files somewhere in the user's PATH.
The executable command must be of the format charm-<plugin name>.

add      error occurred running 'charm-add --description'
build    error occurred running 'charm-build --description'
compose  build: compose has been deprecated, please use build
create   error occurred running 'charm-create --description'
help     usage: charm-help subcommand
layers   error occurred running 'charm-layers --description'
proof    error occurred running 'charm-proof --description'
test     Execute a charms functional tests
version  charm-tools 2.0a1

• charm-add
• charm-build
• charm-compose
• charm-create
• charm-layers
• charm-proof
• charm-test
• charm-version

Need to have --description flag and values.