Create a short Contributing Overview guide (new content)

[jenweber]

It can be tough to know where to get started with contributing to Ember! We should create a short and sweet welcome message and some general guidance for new contributors. Your work will become the first page of the Contributing section of the guides, instead of this page.

To do:

• Copy the contents of contributing/index.md into contributing/adding-new-features.md. Do not make changes to this article, since it's handled in another issue/PR.
• In contributing/index.md, write some basic content following the outline below.
• Open a PR as soon as you have a first draft. It does not need to be perfect. Maintainers will review and request changes if any are needed.

Tips:

• You should only change files in the release directory. You can leave older versions as-is.
• You should expect Percy tests to fail. They check for visual differences, and your writing will cause a difference. Maintainers will review these diffs, so don't worry about them.
• If you need to add words to the spellchecker, search the project for a file that ends in .dict and add them there

Possible outline

You can change this up if you would like! This is just a suggested outline to get you started.

• Intro sentence, something like "Ember is an open source project that succeeds with the help of volunteers. Community members are invited to help out with anything from bug reports to documentation/ This guide will give you some tips on how to get started and where to ask for help if you want to get involved. Thanks in advance for your help!"
• Types of contributions - a short list that encourages people to think outside the box. Contributing to open source is more than code! It includes bug reports, docs, comments on RFCs, etc.
• Where to get started - link to help-wanted. Also suggest that a great place to start is helping improve something you personally ran into. Also link to the list of main repositories that already exists in another page under Contributing
• Asking for help - Encourage commenting directly on issues and PRs. Link to the emberjs.com/community page and encourage people to join discord. Let them know that the channels that start with dev are for contributors working on those projects, and they are a great place for questions.
• Closing word of encouragement - anyone at any skill level can help out

[DanaKirsh]

would like to work on this issue as part of the EmberConf contributors workshop :)