Document Contributing Guidelines

[exedore6]

I think it would help the project (and get more help) if the project was clear on what was the best way to submit features or fixes. See Setting guidelines for repository contributors

[eikek]

Thanks for bringing this up. I'm going to add some guidelines. It's basically this: I appreciate any kind of contributions a lot! If you happen to want to put more time and effort into something, it's better to open an issue first to check back (if you want it to be merged).

[eikek]

I added some here: #430 - if something is missing/not clear let me know. Thanks!