Add peer awareness design document

[hackerwins]

What this PR does / why we need it:

Writing a design document for Peer Awareness.

Which issue(s) this PR fixes:

Fixes #48

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Additional documentation:

Checklist:

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

Merging #139 (71565d5) into master (b00cfe3) will not change coverage.
The diff coverage is n/a.

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  Hits         1739     1739           
  Misses       1056     1056           
  Partials      173      173           

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[dc7303]

This is really cool!
It seems to be well written for easy understanding. I gave some opinions, so please check.

[habibrosyad]

In my opinion, this design document is great, simple and easy to understand.

For design document I think we can introduce more solid and consistent structures (especially later when some collaborator/contributor want to convey their ideas for enhancing yorkie with more features). I thought a good reference for this would be the KEP (Kubernetes Enchancement Proposal), e.g. this one.

[hackerwins]

@dc7303, @habibrosyad Thank you for your review. I adjusted the section to reflect your comments.

Also, @dc7303 commented that the first document will be referenced in future documents, so it's a good idea to handle it carefully. So I added a template too.

[dc7303]

LGTM 👍 I think the written template and the peer-awareness.md document are appropriate as our first design document.

[mojosoeun]

Thank you for your work! The design document and template are awesome and easy to understand! Also, I was able to learn about peer-awareness!