📝 Switch actions/checkout from master to main in README.md (#320)

Author: rasa

README.md

@@ -36,14 +36,15 @@ name: Sync Files
 on:
   push:
     branches:
+      - main
       - master
   workflow_dispatch:
 jobs:
   sync:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@master
+        uses: actions/checkout@main
       - name: Run GitHub File Sync
         uses: BetaHuhn/repo-file-sync-action@v1
         with: