Add documentation so that pwa: commands work

[tacman]

I thought the commands were gone! But they're not even visible if the dependencies aren't installed.

Another approach would be to register the command, but not allow it to run without the dependencies, and simply tell the user what they need to install.

I can make a PR for that if you want.

[Spomky]

This should be in https://pwa.spomky-labs.com instead. Repository is here: https://github.com/Spomky-Labs/phpwa-doc

[Spomky]

Many thanks