Add Oslo feature freeze to release schedule

Oslo freezes one week before non-client library freeze. We need to
note that in the release schedule.

Change-Id: I83713017b29ae900ccc9f3263e483984c3abc440

doc/source/ussuri/schedule.rst

@@ -227,6 +227,17 @@ Ussuri releases for the OpenStack Dashboard plugin (manila-ui) and the
 python SDK / CLI library (python-manilaclient) will be made by the end of
 the week.
 
+Oslo
+----
+
+.. _u-oslo-feature-freeze:
+
+Oslo Feature Freeze
+^^^^^^^^^^^^^^^^^^^
+
+All new Oslo features must be proposed and substantially complete, with unit
+tests by the end of the week.
+
 
 PTL Elections
 -------------

doc/source/ussuri/schedule.yaml

@@ -90,6 +90,8 @@ cycle:
   start: '2020-03-23'
   x-project:
     - u-extra-atcs
+  project-specific:
+    - u-oslo-feature-freeze
 - end: '2020-04-03'
   name: R-6
   start: '2020-03-30'