Add GitHub actions again

.github/workflows/docker.yml

@@ -0,0 +1,33 @@
+name: docker-build
+
+on:
+  push:
+    branches:
+      - '**'
+    tags:
+      - 'v*'
+  pull_request:
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      -
+        name: Login to GitHub Images
+        uses: docker/login-action@v1
+        with:
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      -
+        name: Build and push
+        id: docker_build
+        uses: docker/build-push-action@v2
+        with:
+          push: ${{ github.event_name != 'pull_request' }}
+          tags: ghcr.io/modrinth/daedalus:latest