Mention OCSP UTC fix in changelog. (#6845)

CHANGELOG.md

@@ -15,13 +15,15 @@ Certbot adheres to [Semantic Versioning](https://semver.org/).
 
 ### Fixed
 
-*
+* Certbot uses the Python library cryptography for OCSP when cryptography>=2.5
+  is installed. We fixed a bug in Certbot causing it to interpret timestamps in
+  the OCSP response as being in the local timezone rather than UTC.
 
 Despite us having broken lockstep, we are continuing to release new versions of
 all Certbot components during releases for the time being, however, the only
 package with changes other than its version number was:
 
-*
+* certbot
 
 More details about these changes can be found on our GitHub repo.