Document compatibility process for the HTTP API
Document compatibility process for the HTTP API

GitLab lacked formal documentation around our API, how the versioning
worked and to the numbers meant.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/22693

iiet/iiet-git,jirutka/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,mmkassem/gitlabhq,jirutka/gitlabhq,mmkassem/gitlabhq,jirutka/gitlabhq,axilleas/gitlabhq,dreampet/gitlab,stoplightio/gitlabhq,stoplightio/gitlabhq,axilleas/gitlabhq,jirutka/gitlabhq,stoplightio/gitlabhq,dreampet/gitlab,stoplightio/gitlabhq,dreampet/gitlab,iiet/iiet-git,axilleas/gitlabhq,mmkassem/gitlabhq,dreampet/gitlab,iiet/iiet-git,axilleas/gitlabhq