Missing instructions to update remote fly instance after #364 ⭐ [Documentation] - <title>

[hippalectryon-0]

Description

#364 removed parts of the documentation related to the obsolete fly web-console.

However, part of that documentation was actually relevant for the local console with a hosted instance.

In particular, the current docs is missing the exact line necessary to update the instance from the local terminal:
fly deploy --image actualbudget/actual-server:latest --app your-app-name

(right now it just says "When updates to Actual are released, you’ll need to re-deploy your app to get the latest version.", but for people not used to the fly commandline it's not clear what command should be ran)

Documentation URL

https://github.com/actualbudget/docs/blob/master/docs/install/fly.md