Add releasenote to tag the Tempest for Train release

This commit adds the releasenote to tag Tempest for Train
and needed for version 22.0.0 to release.

Change-Id: Iefd45a14178eb61e5c0a60116e30217fbab0284e
diff --git a/releasenotes/notes/tempest-train-release-a2ed0743a5eadeb6.yaml b/releasenotes/notes/tempest-train-release-a2ed0743a5eadeb6.yaml
new file mode 100644
index 0000000..960b0b2
--- /dev/null
+++ b/releasenotes/notes/tempest-train-release-a2ed0743a5eadeb6.yaml
@@ -0,0 +1,17 @@
+---
+prelude: |
+    This release is to tag the Tempest for OpenStack Train release.
+    This release marks the start of Train release support in Tempest.
+    After this release, Tempest will support below OpenStack Releases:
+
+    * Train
+    * Stein
+    * Rocky
+    * Queens
+
+    Current development of Tempest is for OpenStack Ussuri development
+    cycle. Every Tempest commit is also tested against master during
+    the Ussuri cycle. However, this does not necessarily mean that using
+    Tempest as of this tag will work against a Ussuri (or future release)
+    cloud.
+    To be on safe side, use this tag to test the OpenStack Train release.