Add PR template, Update Changelog and Contributing.md

[ValarDragon]

This PR adds a PR template, and a contributing.md file, and defines the new branch structure.

It also updates the changelog for develop. I've also included what shows on the PR template to reviewers here.

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Before we can merge this PR, please make sure that all the following items have been checked off. If any of the checklist items are not applicable, please leave them but write a little note why.

• [x] Targeted PR against correct branch (develop)
• [ ] Linked to Github issue with discussion and accepted design OR have an explanation that describes this work.
• [x] Wrote unit tests - N/A
• [x] Added a relevant changelog entry to the Pending section in CHANGELOG.md
• [x] Re-reviewed Files changed in the Github PR explorer

[ValarDragon]

Sorry, did not mean to merge this 😰, meant to merge #78 please do leave comments and we can update for them in a different PR.