Fixed issue with RFC-Cron (#69)

It was improperly set to run every minute after 11. I changed it to run
every weekday only once after 12.

Also, added status badge for the job in the Readme so we can preview
there that the job is running:
[![RFC
Cron](https://github.com/polkadot-fellows/RFCs/actions/workflows/rfc-referenda-notifications.yml/badge.svg)](https://github.com/polkadot-fellows/RFCs/actions/workflows/rfc-referenda-notifications.yml)

.github/workflows/rfc-referenda-notifications.yml

@@ -3,11 +3,12 @@ name: RFC Cron
 on:
     workflow_dispatch:
     schedule:
-      - cron: '* 11 * * *'
+      - cron: '0 12 * * 1,2,3,4,5'
   
 jobs:
-  test_run:
+  rfc_notification:
     runs-on: ubuntu-latest
+    name: Notify on referendas
     steps:
         - name: Get last run
           run: |