feat: print link to getting started after installation

[EverlastingBugstopper]

fixes #141 by printing the output of rover --help as long as the user does not need to reload their shell to get rover in their PATH.

if we think it's too much output right away, i'm happy to come up with an alternative solution that's a bit less verbose!

[JakeDawkins]

Nice! I feel like the --help text seems a little verbose as a post-install message. I'm not necessarily opposed, but I feel like it could be annoying to have a wall of text on install rather than a help message. Thoughts on that?

[EverlastingBugstopper]

yeah i also had that reaction - maybe we print the url to the docs if rover isn't in their PATH yet and if it is already there we can print just the line: You can read the getting started guide by running rover docs open start. that seems more manageable to me.

[JakeDawkins]

Agreed, that seems a bit less "in your face"