Copy the upgrade note to 1.26.0.

Author: clokep

CHANGES.md

@@ -1,7 +1,11 @@
 Synapse 1.26.0 (2021-01-27)
 ===========================
 
-No significant changes.
+No significant changes since 1.26.0rc2.
+
+This release brings a new schema version for Synapse and rolling back to a previous
+version is not trivial. Please review [UPGRADE.rst](UPGRADE.rst) for more details
+on these changes and for general upgrade guidance.
 
 
 Synapse 1.26.0rc2 (2021-01-25)
@@ -25,8 +29,8 @@ Synapse 1.26.0rc1 (2021-01-20)
 ==============================
 
 This release brings a new schema version for Synapse and rolling back to a previous
-version is not trivial.  Please review [UPGRADE.rst](UPGRADE.rst) for more details
-on these changes  and for general upgrade guidance.
+version is not trivial. Please review [UPGRADE.rst](UPGRADE.rst) for more details
+on these changes and for general upgrade guidance.
 
 Features
 --------