Extends documentation about commands' phpdoc possibilities/limitations

[drzraf]

• Yes, I reviewed the contribution guidelines.

Describe your use case and the problem you are facing

Commands cookbook is lacking some edge-cases about commands' options and I didn't find my answer in any other place either.

Describe the solution you'd like

I'd like to find answers to the following topics regarding phpdoc definition of a command:

1. Handling short option. Why aren't they supported? Is there known workarounds?
2. Handling options expecting a comma-separated list of values (like in --foo=bar,baz). It's another common case and I failed to find any example. It's sad options couldn't be used and one can't know if some utils already exist within wp-cli to handle them.
3. Multiple occurrences of the same option (like in --regex=ab --regex=cd) is another case where documentation is lacking.