poetry add command doesn't have help #1920

• I am on the latest Poetry version.

• I have searched the issues of this repo and believe that this is not a duplicate.

• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: OS X Sierra

• Poetry version: 1.0.2

Issue

If I run poetry without any arguments, I get a help screen with a list of commands. If I run poetry with a command and --help flag, like poetry show --help I get a help screen for that command. This does not seem to be the case for add command. Running poetry add --help results in an error message Not enough arguments (missing: "name"). and that is it. Would be nice to have a help screen for add command.