Create CONTRIBUTING.md

[kstine]

Create a document for rules for submitting work items in the style guide.

See example: https://github.com/robotframework/robotframework/blob/master/CONTRIBUTING.rst

Leverage the Good First Issue and Help Needed Label from Github (actually use it)

Edit Page button at bottom of guides pages.

Paths to contributing:

• Create an issue in github
• Work on an issue (github process outlined via chart)
• Simple Edits Edit Page

[Mko13]

Remember to update the link to the Issues on the RF Docs website, if we move the Issues from current repo to the Guides repo.