Add release management guide for PMCs

[asfimport]

The Arrow release process has grown increasingly complex and time consuming, and there are many manual steps that a release manager must undertake before, during, and after a release vote. I will write a document to list all of these. Some of them desperately need to be more automated (like updating the online API documentation and website). Binary packaging is still not as automated as it could be.

Reporter: Wes McKinney / @wesm
Assignee: Wes McKinney / @wesm

PRs and other links:

• GitHub Pull Request #1185

_{Note: This issue was originally created as ARROW-1635. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Issue resolved by pull request 1185
#1185