add GitHub action to update assets

.github/workflows/update-assets.yml

@@ -0,0 +1,17 @@
+name: Plugin asset/readme update
+on:
+  push:
+    branches:
+    - master
+jobs:
+  master:
+    name: Push to master
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - name: WordPress.org plugin asset/readme update
+      uses: 10up/action-wordpress-plugin-asset-update@master
+      env:
+        SVN_PASSWORD: ${{ secrets.SVN_PASSWORD }}
+        SVN_USERNAME: ${{ secrets.SVN_USERNAME }}
+        SLUG: activitypub

.svnignore

@@ -7,6 +7,7 @@
 .codeclimate.yml
 .data
 .svnignore
+.wordpress-org
 Gruntfile.js
 LINGUAS
 Makefile