Change docs instructions from using 'templates' as submodule

[cometsong]

Usage descriptions of the flowcraft/templates folder as a submodule need to be updated/removed.

As I followed the directions to find out more, I realized the repo code had been updated to include the folder natively and not to use submodule anymore.

1. I first found the submodule mentioned in dev docs "General Orientation" -> codebase -> templates section, as defined in the rst file

2. "How to use as a submodule" in template README

3. Developer installation as defined in the rst file

I can do a PR for this, if that works for you.

(Currently I'm working on a set of new process generator templates as well, for other PR's.)

[cimendes]

Hello! Thank you for noticing that! I had the idea that that particular step was already updated, but thanks for catching it! Indeed the folder is packaged together with the flowcraft code. I'll try to get it fixed later this evening.

I've very happy that you're interest in contributing with new templates. All code contributions are very welcomed. Feel free to join our gitter chat, or to contact me by e-mail if need be (cimendes@medicina.ulisboa.pt)!