docs: integrate Musikus Discord server (#106)

Add a GitHub workflow which publishes newly opened PRs and releases to our Discord server via a webhook.

Link Discord server in readme.

.github/workflows/discord-webhook.yml

@@ -0,0 +1,29 @@
+name: DISCORD-WEBHOOK
+
+on:
+  pull_request:
+    types: [opened]
+  release:
+    types: [published]
+
+jobs:
+  notify-discord:
+    name: Notify Discord
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Send Discord notification for PR
+        if: github.event_name == 'pull_request'
+        run: |
+          curl -H "Content-Type: application/json" \
+          -X POST \
+          -d "{\"content\": \"📣 **New Pull Request**: [${{ github.event.pull_request.title }}](${{ github.event.pull_request.html_url }})\n\n📝 **Description**: ${{ github.event.pull_request.body }}\n\n🚀 **Branch**: ${{ github.event.pull_request.head.ref }}\"}" \
+          ${{ secrets.DISCORD_WEBHOOK_URL }}
+
+      - name: Send Discord notification for Release
+        if: github.event_name == 'release'
+        run: |
+          curl -H "Content-Type: application/json" \
+          -X POST \
+          -d "{\"content\": \"🎉 **New Release**: [${{ github.event.release.name }}](${{ github.event.release.html_url }})\n\n📦 **Version**: ${{ github.event.release.tag_name }}\n\n📝 **Description**: ${{ github.event.release.body }}\"}" \
+          ${{ secrets.DISCORD_WEBHOOK_URL }}

README.md

@@ -20,12 +20,20 @@ Your personal practice companion
 
 ## 🧪 Musikus is in alpha
 
-### Join
+### Become a tester
 If you want to join our group of testers, write us an email to [[email protected]](mailto:[email protected]) using your Gmail-account and we will add you to the list.
 
 ### Feedback
 If you have any feedback, bug reports or feature requests, please fill out [this](https://docs.google.com/forms/d/e/1FAIpQLSfw1rTslL7b3Yp_Lv_E65zketfj7G6h5VzOkVdxjcQZDC5CqA/viewform) form or use the [Issue Tracker](https://github.com/matthiasemde/musikus-android/issues/new).
 
+## 🤝 Join Our Community on Discord
+
+We're happy to invite all music and coding enthusiasts to our Discord server! This is your space to collaborate, share insights, and help shape the future of Musikus. 🚀
+
+[Join the Musikus Discord Server](https://discord.gg/CNbvGmbS7d)
+
+Whether you're looking to contribute code, discuss features, or just want to chat about music or code, our Discord server is the perfect place to be. See you there! 👋
+
 ## 👨‍💻 Contributors
 <a href="https://github.com/matthiasemde/musikus-android/graphs/contributors">
   <img width="140" src="https://contrib.rocks/image?repo=matthiasemde/musikus-android" alt="https://github.com/matthiasemde/musikus-android/graphs/contributors"/>