Added docker workflow

.github/workflows/docker.yml

@@ -0,0 +1,17 @@
+name: Build CME Docker Image
+
+on: [push]
+
+jobs:
+    build:
+      runs-on: ubuntu-latest
+      steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+      - name: Build Docker Image and Publish to Github Packages
+        uses: whoan/docker-build-with-cache-action@v5
+        with:
+          username: ${{ secrets.GIT_USERNAME }}
+          password: ${{ secrets.GIT_TOKEN }}
+          registry: docker.pkg.github.com
+          image_name: crackmapexec