Hacky fix for Reno removing 0.16+ release notes (#1479) (#1480)

Co-authored-by: Arnau Casau <[email protected]>

docs/release_notes.rst

@@ -1,2 +1,13 @@
+.. 
+  For some reason, Reno stopped including release notes
+  for 0.16+ starting on the stable/0.21 branch. We can get
+  things working by using two release-note entries. The
+  API conversion in qiskit/documentation will merge these two
+  lists together. Refer to
+  https://github.com/Qiskit/documentation/issues/978
+
 .. release-notes:: Release Notes
+  :earliest-version: 0.16.0
+
+.. release-notes:: HACK FOR RENO ISSUE
   :earliest-version: 0.1.0rc1