ci: add simple github action for building image, running crawl, verifying zim exists

.github/workflows/ci.yaml

@@ -0,0 +1,19 @@
+name: CI
+
+on: [push, pull_request]
+
+jobs:
+  integration-tests:
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v2
+
+      - name: build image
+        run: docker build -t openzim/zimit:dev .
+
+      - name: run crawl
+        run: docker run -v $PWD/output:/output openzim/zimit:dev zimit --url https://isago.ml/ --name isago --zim-file isago.zim
+
+      - name: ensure zim exists
+        run: stat ./output/isago.zim