Add GCP docs

docs/docs/postgresql/source-database.md

@@ -270,6 +270,18 @@ The Reader endpoint will continue to be available without downtime.
 
 See the [AWS RDS user guides](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_WorkingWithParamGroups.html) to learn more about parameter groups.
 
+### GCP Cloud SQL
+
+#### WAL level {#gcp-wal-level}
+Logical replication is turned off by default. To turn it on, you have to update the [cloud flag](https://cloud.google.com/sql/docs/postgres/replication/configure-logical-replication#configure-your-postgresql-instance): `cloudsql.logical_decoding` = `on`. This will need a restart of your instance before `SHOW wal_level;` returns `logical`. 
+
+#### Connection {#gcp-connection}
+Run the below command and then you can connect with the same credentials on the Bemi dashboard! 
+```sql
+-- Grant replication permission to allow using replication slots
+ALTER USER [user] WITH REPLICATION;
+```
+
 ### Self-managed PostgreSQL
 
 #### Connection {#self-managed-connection}