Incorrect Sync Gateway info in upgrade docs

When a customer upgrades from 4.x, the matrix implies they need to go specifically to 5.0. It's not true, they can upgrade to the latest 5.x release. I got asked this question several times already.

Also, it may be a good idea to include a link or a mentioning about how Sync Gateway configs need to be updated when customers switch from CB Server 4.x to 5.x due to RBAC. For each database reference in config.json file, there are now username and password fields (https://docs.couchbase.com/sync-gateway/2.1/config-properties.html). We used to have bucket passwords instead.

Reporter: Oleg Kuzmin
E-mail: oleg.kuzmin@couchbase.com