More description with releases
More description with releases

- Describes that release activities are mainly related with
  cycle-with-milestone release model projects and translation
  targets
- Documentation in openstack-manuals follows independent
  release model and project repositories can have stable branch
  documents. Let's describe this.
- Also, explains that other official project can be a release
  target to I18n team upon request assuming that there is a
  cross-project liaison to I18n team.

Change-Id: Ibbcf797b11a58fb57b7dd044d1d6948ce5b06cbc

openstack/i18n,openstack/i18n