nix-shell environment and basic drone ci config

.drone.yml

@@ -0,0 +1,8 @@
+kind: pipeline
+type: exec
+name: default
+
+steps:
+  - name: build
+    commands:
+      - nix-shell --pure --run "flutter build apk --split-per-abi"

shell.nix

@@ -0,0 +1,5 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.mkShell {
+  nativeBuildInputs = [ pkgs.flutter ];
+}