Add link to how-to-jdk-update in notification

.github/workflows/check-jdk-updates.yml

@@ -58,7 +58,7 @@ jobs:
           SLACK_ICON: false
           SLACK_ICON_EMOJI: ':bot:'
           SLACK_CHANNEL: 'cryptomator-desktop'
-          SLACK_TITLE: "JDK update"
-          SLACK_MESSAGE: "Cryptomator-CI JDK can be upgraded to ${{ needs.jdk-latest.outputs.jdk-version }}"
+          SLACK_TITLE: "JDK update available"
+          SLACK_MESSAGE: "Cryptomator-CI JDK can be upgraded to ${{ needs.jdk-latest.outputs.jdk-version }}. See https://github.com/cryptomator/cryptomator/wiki/How-to-update-the-build-JDK for instructions."
           SLACK_FOOTER: false
-          MSG_MINIMAL: true
+          MSG_MINIMAL: true