Upgrade guidelines

[Laith-jalal]

Hi,
I have been checking the usage.md and config.md in order to upgrade my PGbouncer, I got a little bit lost in how to perform the upgrade without dropping the connections.
Do I find a document that explains the upgrading process?

[JelteF]

Currently there is no way of performing an in place upgrade without dropping connections, but that is going to be improved with this PR once it's merged: #902

You can do upgrades if you have multiple nodes with a load balancer in front. And create new nodes with the new version, and add them to the load balancer and then drain the existing nodes before disconnecting them.