Move documentation to doc directory

[kazuhitoyokoi]

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Proposed changes

I moved v0.0.2 documentation from wiki to docs directory.
Using docs directory instead of wiki, users can read appropriate documentation for each version.

Checklist

• I have read the contribution guidelines
• For non-bugfix PRs, I have discussed this change on the mailing list/slack team.
• I have run grunt to verify the unit tests pass
• I have added suitable unit tests to cover the new/changed functionality

[coveralls]

Coverage remained the same at 77.812% when pulling 63d14cb on kazuhitoyokoi:master-movedocs into 6b88422 on node-red:master.