Docs: empty string compare rule

[oraNod]

Add MD documentation for the empty_string_compare rule.

[ssbarnea]

@oraNod it is much better to make the change atomic (per rule), even if that means opening 10 pull requests. While I made few fixes on your change I observed that the no-handler docs and change seems wrong and I would like to remove it from this change, but that is not so easy if everything is in a bundle.

[oraNod]

@ssbarnea Do you want me to break this one into multiple PRs too? Or was it just moving the no_handler rule to a separate PR?

[ssbarnea]

@oraNod If you can split it it would be awesome as it would make much easier to review, update and merge them one by one.

Some of them would be harder to review and we want to merge the easy ones ASAP.

[oraNod]

@ssbarnea Sounds good. I'll do that today, just wasn't sure as you mentioned in chat you might just merge this one. Thanks!