feat(ci): add CI

.github/dependabot.yml

@@ -0,0 +1,8 @@
+version: 2
+
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+

.github/workflows/ci.yaml

@@ -0,0 +1,15 @@
+name: ci
+
+on:
+  push:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/[email protected]
+      - uses: DeterminateSystems/nix-installer-action@v11
+      - uses: DeterminateSystems/magic-nix-cache-action@main
+      - name: Build package
+        run: nix build -L
+

README.md

@@ -1,5 +1,7 @@
 # magit-file-icons.el
 
+<img src="https://img.shields.io/github/actions/workflow/status/gekoke/magit-file-icons/ci.yaml?style=for-the-badge"/>
+
 Display file icons in ![Magit](https://github.com/magit/magit)!
 
 # Preview