Add Android AAR workflow

.github/workflows/aar.yaml

@@ -0,0 +1,21 @@
+name: Build Android AAR
+
+on: [workflow_dispatch]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Checkout submodules
+      run: git submodule update --init
+
+    - name: Build
+      run: ./build.sh android-aar "release"
+
+    - uses: actions/upload-artifact@v2
+      with:
+        path: dist
+