Added release date

Added release date.
Signed off by: Saju <sajmoham@redhat.com>

Author: msaju

docs/release-notes/8.1.md

@@ -1,5 +1,7 @@
 # Release notes for Gluster 8.1
 
+**Release date:** 27-Aug-2020
+
 This is a Improvements and bugfix release. The release notes for [8.0](8.0.md)
 contains a listing of all the new features that were added
 and bugs fixed in the GlusterFS 8 stable release.