Create CONTRIBUTING.md guidelines file

[mihok]

As we try to promote more community members helping with the site, I think it makes sense we should include a CONTRIBUTING.md file.

My thoughts are even though some of these things should be fairly obvious if you have worked in OSS before, we should be explicit. This is a chance for us to be a "guiding light" for newcomers to learn about open source development and get involved.

• We should highlight the development process. (fork > branch your local repo > code/commit/push local repo > create PR with torontojs repo, etc)
• Create issues (if they dont already exist) for discussion on reasonably large implementation and/or changes
• We should speak about assigning recommended reviewers (probably @alex-wilmer and @tazsingh or one of the organizers?)
• Link to the tojs-styleguide (and update it if necessary)
• Explain anything unique in the design/architecture

Lets discuss anything here that we're not aligned on or that I'm missing

I'm happy to build out the document if @alex-wilmer is available to probe for any questions regarding design/architecture

(cc: @dxnn @pauldowman)

[dxnn]

This is a fantastic idea! Happy to help review PRs etc when I can.