Streamline installation via `asdf`

[lindhe]

Checklist

• [x] I have signed the CLA
• [x] I have updated/added any relevant documentation

Description

This change removes the step of manually listing versions with asdf and instead uses the latest keyword to install latest version.

[CLAassistant]

All committers have signed the CLA.

[lindhe]

Sorry for creating an unsolicited PR like this, but it was easier and quicker to create a PR than to first create an issue and ask if this is a good idea. If you want to reject my PR, that's fine – it's just a minor change that bugged me when installing pluto for the first time.