[Feature Request] Check and inform user when newer version is available

Is your feature request related to a problem? Please describe.

I don't always remember to check this repo to see if a newer version is available, and so just recently spent a bunch of time investigating an issue that turns out to have been solved since I last upgraded. In retrospect, "check before you test" may be somewhat reasonable while this project is <1.0, but as the time between versions inevitably increases, users will more frequently end up in the same "oh shoot, I should have checked for upgrades first" camp as I did.

Describe the solution you'd like

A message or similar output on start or on --version that informs of new releases of the CLI. Added bonus: a built-in self-upgrade command. Alternate: like the pip example below, include the command to upgrade in the output for easy copy-pasta.

Additional context

The message I'm envisioning is similar to what pip gives:

[notice] A new release of pip is available: 23.0.1 -> 23.1.2
[notice] To update, run: pip install --upgrade pip