Move release team ladder & infra into proper page

The release team involvement ladder and infrastructure primer were
hard to find in CONTRIBUTING.rst. It's better to move them next to
the rest of the team documentation.

Change-Id: I3859ce431711cef5176a3ea34b9433bd06d51447

doc/source/index.rst

@@ -174,7 +174,9 @@ documentation:
    reference/using
    reference/release_models
    reference/deliverable_types
+   reference/join_release_team
    reference/reviewer_guide
+   reference/release_infra
    reference/process
 
 .. _`openstack/releases`: https://opendev.org/openstack/releases

doc/source/reference/join_release_team.rst

@@ -0,0 +1,61 @@
+======================
+Join the release team!
+======================
+
+Communication channels
+======================
+
+The release team communicates and meets on the `#openstack-release`_ channel
+on OFTC IRC, on the `openstack-discuss mailing-list`_ using the [release]
+subject prefix.
+
+.. _`#openstack-release`: https://webchat.oftc.net/?channels=openstack-release
+
+.. _`openstack-discuss mailing-list`: http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-discuss
+
+The engagement ladder
+=====================
+
+Getting involved with release management can feel a bit overwhelming.
+To set expectations reasonably, we define 4 levels of engagement.
+
+Stage 0 - Review release requests
+---------------------------------
+
+This stage does not require any special rights. You should just review
+release requests (modifications of files in deliverables/ directory in
+the releases repository), apply the release review rules and vote.
+
+See the :doc:`reviewer_guide` for more review guidelines.
+
+Stage 1 - Approving release requests
+------------------------------------
+
+At this stage you will be trusted with CodeReview+2 and Workflow+1 votes
+on the releases repository, giving you the ability to trigger releases.
+You will need a base understanding of the :doc:`release_infra`, and know
+to refrain from approving when unsure.
+
+Checklist before approving a release:
+
+* You should only approve release requests.
+* You should check that release is approved by PTL or release liaison
+* You should check that infrastructure is not currently experiencing issues
+* You should check that we are not in any freeze period
+* If unsure, it is better to wait for a second opinion that to press
+  Workflow+1 directly.
+
+
+Stage 2 - Knowing the release cycle process
+-------------------------------------------
+
+At this stage you will be able to help drive the release cycle process,
+send reminder emails and answer questions from release liaisons.
+
+
+Stage 3 - Understanding the Release Automation Infrastructure
+-------------------------------------------------------------
+
+At this stage you will be able to debug complex :doc:`release_infra`
+failures, and review/approve release tooling changes.
+

doc/source/reference/release_infra.rst

@@ -0,0 +1,54 @@
+======================
+Release infrastructure
+======================
+
+What happens when a release is approved? Release infrastructure is divided
+into two steps, triggered by different, but related events.
+
+The first step is triggered by the release request being merged into the
+releases repository, starting a series of jobs in the "post" pipeline
+of the releases repository::
+
+  Release request merged
+              |
+      +-------v-----------------------+
+        Post pipeline (releases repo)
+      +---+-----------------------+---+
+          |                       |
+          v                       v
+  +-------+-------+       +-------+-------+
+  |      tag      |       |  publish-docs |
+  |               |       |               |
+  | (pushes tags  |       | (to releases  |
+  | to each repo) |       |     website)  |
+  |               |       |               |
+  +-------+-------+       +---------------+
+
+The second step is triggered by the creation of the tag, creating a series
+of jobs in the "tag" pipeline and the "release" pipeline (or "pre-release"
+pipeline, in case of beta versions) of the repository the tag landed in::
+
+  Tag is created -----------------------------------------------
+        |                                                      |
+   +----v------------------------------------+      +----------v-----------+
+          Release pipeline (each repo)              Tag pipeline (each repo)
+   +----+---------------+---------------+----+      +----------------------+
+        |               |               |                      |
+        v               v               v                      v
+  +-----+-----+   +-----+-----+   +-----+-----+          +-----+-----+
+  |  release  |   |  announce |   |  propose  |          |  publish  |
+  |           |   |           |   |constraints|          |  release  |
+  |(builds    |   |  (sends   |   |  update   |          |  notes    |
+  | tarball   |   |   email)  |   |           |          |           |
+  | & uploads |   |           |   +-----------+          +-----------+
+  | it)       |   +-----------+
+  +-----------+
+
+Note that a single release request can create multiple tags in different
+repositories, triggering that second stage in multiple repositories.
+
+Jobs in the release pipeline need information from the release request
+(like series name, or whether to upload to pypi). We use metadata in the
+git tag itself to pass that information: the "tag" job in step 1 records
+the information in the tag, and the jobs in step 2 retrieve that information
+directly from the tag.