implement basic action for builds and updates

.github/workflows/main.yml

@@ -0,0 +1,42 @@
+name: main
+on: push
+jobs:
+  main:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Repository
+      uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+    - name: Variables
+      id: variables
+      run: echo ::set-output name=version::$(git describe --tags --always)
+    - name: Java
+      uses: actions/setup-java@v1
+      with:
+        java-version: 11
+    - name: Secrets
+      run: echo "${STORE_DATA}" | base64 --decode > store.jks
+      env:
+        STORE_DATA: ${{ secrets.STORE_DATA }}
+    - name: Build
+      uses: eskatos/gradle-command-action@v1
+      env:
+        STORE_PASSWORD: ${{ secrets.STORE_PASSWORD }}
+        KEY_ALIAS: ${{ secrets.KEY_ALIAS }}
+        KEY_PASSWORD: ${{ secrets.KEY_PASSWORD }}
+      with:
+        arguments: assemble
+        gradle-version: 6.7.1
+    - name: Move
+      run: mv app/build/outputs/apk/release/*.apk gelli-release-${version}.apk
+      env:
+        version: ${{ steps.variables.outputs.version }}
+    - name: Publish
+      if: startsWith(github.ref, 'refs/tags')
+      uses: ncipollo/release-action@v1
+      with:
+        artifacts: '*.apk'
+        tag: ${{ steps.variables.outputs.version }}
+        commit: ${{ github.sha }}
+        token: ${{ github.token }}