docs: add install instructions for nixpkgs (#2401)

* docs: add install instructions for nixpkgs

I also included the link to the package in NixOS Search btw.

* docs: remove nixos config notes per #2401 (comment)

docs/installing-with-package-manager.md

@@ -45,6 +45,25 @@ emerge app-editors/lapce
 brew install lapce
 ```
 
+### nixpkgs
+
+You can find the packages [here](https://search.nixos.org/packages?channel=unstable&show=lapce&from=0&size=50&sort=relevance&type=packages&query=lapce):
+
+```bash
+# try with nix-shell
+nix-shell -p lapce
+
+# on NixOS
+nix-env -iA nixos.lapce
+
+# on non-NixOS installs, including macOS
+nix-env -iA nixpkgs.lapce
+
+# only if nix.settings.experimental-features is set to both "nix-command" and "flakes"
+# WARNING: THIS BREAKS nix-env, PROCEED AT YOUR OWN RISK. THIS ALSO INSTALLS FROM UNSTABLE BRANCH.
+nix profile install nixpkgs#hello
+```
+
 ### Scoop
 
 ```bash