Add update checker

.github/workflows/main.yaml

@@ -4,6 +4,8 @@ on:
   push:
     tags:
     - '*'
+  repository_dispatch:
+    types: update
 
 env:
   DOCKER_TAG: shenxn/protonmail-bridge

.github/workflows/update-check.yaml

@@ -0,0 +1,22 @@
+name: update check
+
+on:
+  push:
+    branches:
+    - update-check
+  schedule:
+  - cron: '0 0 * * *'  # runs everyday at midnight
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout
+      uses: actions/checkout@master
+      with:
+        ref: master
+    - name: Check Update
+      run: bash check-update.sh
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        PERSONAL_TOKEN: ${{ secrets.PERSONAL_TOKEN }}