Add a panic handler that links people to the New Issue form on Github when the app crashes.

[capnfabs]

I still don't have 100% confidence that I've covered all edge cases for Git handling in my code, so if someone runs into a problem, It'd be nice if they could report that easily.

Having said that, I've received bug reports from users without building this functionality, so I think it's a nice-to-have instead of a necessity.

[jasikpark]

Nice! So just throw "https://github.com/capnfabs/grouse/issues/new" in the error text, right?

I'm glad that you got .GitInfo working! Currently I use percy a lot but I only get 5,000 screenshots a month for free, and when it gets called 100 times in a day, it's surprisingly easy to burn through that.

I'm excited to get this set up on my site!

I feel like a github action would be good too... maybe I can figure out how that all works

[capnfabs]

@jasikpark I think people have used Grouse with CI before! Notably #12 seems to have been prompted by this.