Check for updates

[fluffy-critter]

What is the problem you are trying to solve?

GUI should be able to check for version updates

What solution would you like?

At startup, phone home to itch.io to check for a newer version or something, and if so, pop up a "update available" dialog.

What alternatives have you considered?

A clear and concise description of any alternative solutions or features you've considered.

What usage mode does this apply to?

Does this affect CLI, desktop, library? Is it OS-specific?

Additional context

Add any other context or screenshots about the feature request here.