add codeberg mirroring CI

.github/workflows/codeberg-mirror.yaml

@@ -0,0 +1,17 @@
+# Sync repo to the Codeberg mirror
+name: Mirror Sync
+
+# on: [push, pull_request, issues]
+on: push
+
+jobs:
+  codeberg:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - uses: pixta-dev/repository-mirroring-action@v1
+        with:
+          target_repo_url: "git@codeberg.org:Xirscz7M2t/darkfi.git"
+          ssh_private_key: ${{ secrets.CODEBERG_SSH_PRIVATE_KEY }}