flake.lock questions

[valencik]

When a user generates a template and uses the provided flake.nix via nix develop (see https://github.com/typelevel/typelevel-nix for more details) it generates a flake.lock file.

1. Should the user be encouraged to commit this file to their git repo?
   Judging from https://github.com/http4s/http4s/blob/series/0.23/flake.lock the answer is yes, we should commit the lock file to the repo.

2. Should we be templating the lockfile for the user so it's generated as part of the giter8 init process?
   If not, I think we ought to add a little mention of the expectations to the outer README here.

cc. @rossabaker

[armanbilge]

Linking to typelevel/sbt-typelevel#109 if there's anything we can/should upstream.