Document MSRV

[aftix]

It would be nice (for the library-part at least) to document/enforce a minimum supported rust version somewhere.

[mattwparas]

That is a great idea. I just ran cargo msrv find at the workspace level and found this:

esult:
   Considered (min … max):   Rust 1.56.1 … Rust 1.83.0
   Search method:            bisect
   MSRV:                     1.76.0
   Target:                   x86_64-unknown-linux-gnu

This checks out since for a while I was developing against 1.76. I'll make a note (and leave this open) while I get this into a workflow and documented