Update documentation to prepare for first release

[sarob]

PR Checklist

• [ X] briefly describe the changes in this PR

Impacts

Administrative documents

List of changes / questions for the ReleaseGuidelines.md as it was created from the mobility-data-specification/ReleaseGuidelines.md:

• Attempted to not make any broad changes, rather small updates.
• This will need the Lacuna steps of publishing releases.
• Can we start publishing packages this release?
• Removed schema update step
• Removed “Given that MDS is stabilizing under MAJOR version 0.x right now, it should be assumed that MINOR version increments (e.g. 0.2.0 to 0.3.0) are equivalent to MAJOR version increments and may contain breaking changes.”
• Ongoing version support: are we supporting two concurrent (MINOR) versions?
• Goal section accurate?
• Primary branches section accurate?
• Backporting changes section accurate?
• Maintaining ReleaseNotes.md seems like a good idea. Are there notes somewhere so I can create an up to date ReleaseNotes.md to start from here?

CONTRIBUTING.md and CODE_OF_CONDUCT.md are copies of the mobility-data-specification files

[schnuerle]

I am going to merge this to the develop branch. It adds 2 files that are pulled from MDS files (CONTRIBUTING.md and CODE_OF_CONDUCT.md). Eventually these will go into the new governance repo but are fine here now. The other file is ReleaseGuidelines.md which is a good start - the rest of it will be added in the #249 PR as needed.