Add changelog for sancho-2-3-0

Author: kderme

cardano-db-sync/CHANGELOG.md

@@ -18,6 +18,11 @@ Some useful links (adjust the numbers to the correct tag):
 
 In the schema docs, you can search for `13.2` or `Conway` for schema changes from the previous official release.
 
+### sancho-2.3.0
+- is compatible with node 8.7-pre
+- introduces flag `--only-gov` which allows db-sync to sync only the governance related data.
+- disable swagger in smash server temporarily
+
 ### sancho-2.2.0
 - is compatible with node 8.6-pre
 - `governance_action.ratified_epoch` is now populated