Add Extra ATC during R-7

This cross-project event seems to be forgotten and it will coming soon [1].
We will start to communicate about this during R-8, these changes
ensure that our calendar is aligned with our needs.

[1] https://releases.openstack.org/reference/process.html#r-7-week-extra-atc-deadline-week
[2] https://releases.openstack.org/reference/process.html#r-8-week

Change-Id: I055cdcdd4c2ef1dab4040eccbc5107cf42e92eb9

doc/source/wallaby/schedule.rst

@@ -77,6 +77,19 @@ second milestones as well as the third milestone, are therefore not considered
 part of the release for the cycle. This does not apply to cycle-trailing
 packaging / lifecycle management projects.
 
+.. _w-extra-atc-freeze:
+
+Extra-ATC freeze
+--------------------------------------
+
+All contributions to OpenStack are valuable, but some are not expressed as
+Gerrit code changes. That allow teams to list active contributors to their
+projects and who do not have a code contribution this cycle, and therefore won't
+automatically be considered an Active Technical Contributor and allowed
+to vote. This is done by adding extra-atcs to
+https://opendev.org/openstack/governance/src/branch/master/reference/projects.yaml
+before the Extra-ATC freeze on 25 February, 2021.
+
 .. _w-final-lib:
 
 Final release for non-client libraries

doc/source/wallaby/schedule.yaml

@@ -89,6 +89,8 @@ cycle:
 - end: '2021-02-26'
   name: R-7
   start: '2021-02-22'
+  x-project:
+    - w-extra-atc-freeze
   project-specific:
     - w-oslo-feature-freeze
 - end: '2021-03-05'