Contributor guidelines

[fedgiac]

We should introduce contributor guidelines.

They could include:

• in which issue/prs we are looking for contributions (`help wanted tag?)
• code style (loosely follow Natspec?)
• expectations on git (avoid rebase, small PRs?)

and anything else I'm probably forgetting about.

We already had a contributor who was interested in them but we couldn't provide any.

[yomanthunder]

@fedgiac i think these will be great for starting of , it would be great if there would be a community channel on telegram or discord where we can discuss about pr , share resources etc (as discussing on GitHub can be inefficient )