Document permissions, channels, etc. in Charmhub login

[lengau]

What needs to get done

Improve the charmcraft login command documentation (https://juju.is/docs/sdk/charmcraft-login) to provide information about what permissions are needed for what, how channels should be specified, etc.

Why it needs to get done

These are frequent questions we get in Matrix that often result in a lot of back & forth because we (the starcraft team) don't remember either.

[syncronize-issues-to-jira]

Thank you for reporting us your feedback!

The internal ticket has been created: https://warthogs.atlassian.net/browse/CRAFT-2827.

This message was autogenerated

[lengau]

Example user question: https://matrix.to/#/!LhFxJIPEcCacgdMghH:ubuntu.com/$8H9jS7bcHtBU-TojeypRiLpktVk17QswKLBpedfshZM

[tim-hm]

It might also need to be updated here https://juju.is/docs/sdk/remote-env-auth where the naked track is given in the example: $ charmcraft login --export=secrets.auth --charm=my-super-charm --permission=package-manage --channel=edge --ttl=2592000