Update README.md

Add usage example for devenv.sh

README.md

@@ -2,3 +2,43 @@
 
 This repository is made for fixing issues with flutter in nixpkgs, specifically [#260278](https://github.com/NixOS/nixpkgs/issues/260278).
 
+# Getting started
+
+This flake provides the following packages:
+
+- packages.${system}.flutter
+- packages.${system}.dart
+- packages.${system}.flutter-unwrapped
+
+Will add overlays later.
+
+## With [devenv](https://devenv.sh)
+
+```yaml
+# devenv.yaml
+inputs:
+  nixpkgs:
+    url: github:NixOS/nixpkgs/nixpkgs-unstable
+  flutter-nix:
+    url: github:maximoffua/flutter.nix
+```
+
+```nix
+# devenv.nix
+{
+  pkgs,
+  inputs,
+  ...
+}: let
+  system = pkgs.stdenv.system;
+  flutter = inputs.flutter-nix.packages.${system}.flutter;
+in {
+  languages.dart.enable = true;
+  languages.dart.package = flutter;
+
+  enterShell = ''
+    flutter --version
+  '';
+}
+```
+