Add NixOs installation instructions to README.md

[rsniezek]

Extend README.md with instructions on how to try and install the lazygit on NixOs.

• PR Description
  Just README.md update, no code changes.

• Please check if the PR fulfills these requirements

• Cheatsheets are up-to-date (run go generate ./...)
• Code has been formatted (see here)
• Tests have been added/updated (see here for the integration test guide)
• Text is internationalised (see here)
• Docs (specifically docs/Config.md) have been updated if necessary
• You've read through your own file changes for silly mistakes etc

[rsniezek]

@jesseduffield Feedback would be apprecieated, thank you!

[karimkhaleel]

From my limited knowledge of nix and NixOS, this checks out.

[stefanhaller]

OK, thanks. I'm happy to merge this, but please don't merge master into your branch. This creates a messy git history that we don't want here. Rebase onto master instead.

(It's not possible to fix this now within lazygit because it insists on using the --rebase-merges option when you rebase, but you can fix it on the command line by saying git rebase --no-rebase-merges master.)

[rsniezek]

OK, thanks. I'm happy to merge this, but please don't merge master into your branch. This creates a messy git history that we don't want here. Rebase onto master instead.

(It's not possible to fix this now within lazygit because it insists on using the --rebase-merges option when you rebase, but you can fix it on the command line by saying git rebase --no-rebase-merges master.)

Done. Added also the nix-flake enabled way to the readme. Cheers!

[stefanhaller]

Nice, thanks. I took the liberty of force-pushing again to remove a trailing space (I'm picky about things like this...)

[rsniezek]

Nice, thanks. I took the liberty of force-pushing again to remove a trailing space (I'm picky about things like this...)

No issue, your playground, your rules :)

Thanks for merging