Update Github contributions instructions

[rogerhoward]

Our current Github flow doesn't require any particular adherence to naming conventions - it's too loose. Let's agree on some basic standards.

[rogerhoward]

1 - Everything must start with an issue...

Issues should have useful, concise titles and enough of a description to understand the scope of the issue.

[rogerhoward]

2 - branches should link to individual issues, and be named using consistent syntax:

bug/#123-abbreviated-issue-title
feature/#123-abbreviated-issue-title
enhancement/#123-abbreviated-issue-title

[rogerhoward]

3 - a branch should represent an atomic change

...merging the branch to master should not break anything in master. A branch should be fully testable and functional once finished - I should be able to deploy any given branch and have a functional site.

[rogerhoward]

4 - pull requests may not be merged by the requester. Ever.

Even me...

[rogerhoward]

5 - once a pull request is merged, the branch should be removed.

Just basic cleanup.

[rogerhoward]

6 - PR's should use Github keywords so they automatically link to/close related issues.

For reference: https://help.github.com/articles/closing-issues-via-commit-messages/