README Rewrite

[timsehn]

The current README has not changed substantially since we took over this project three years ago. We should rewrite the README to reflect the current state of the project.

[jycor]

There's a script Zach made me write a while back that somewhat updates the README (just the sql function counts)
https://github.com/dolthub/go-mysql-server/blob/main/scripts/generate_readme.go

[timsehn]

@zachmu did this.