Add contributing guidelines for specification issues and MRs
The project's contributing guide should:
- link to and describe the project's communication channels
- describe the legal considerations for contributors, including the ECA and signing commits
- link to the project scope and release plan
- specify what policies apply to the project, including the Code of Conduct, Eclipse IP policy, and EFSP
- describe the information that should be provided in specification issues
- describe/link to how the project makes decisions
- lay out specification merge request guidelines and processes
- provide instructions for setting up a local repository
- list the workflow steps for creating an issue branch and submitting a MR
This issue only focuses on contributions for the specification, not the end user documentation. A separate issue and MR should focus on the end user documentation contributing process.