docs(readme): note that AZURE_CREDENTIALS is DM'd over Slack

Add a brief Task 7 callout above the tasks table so students know where
the AZURE_CREDENTIALS JSON will come from (cohort-wide secret, distributed
by the teacher over Slack DM).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Lasse Benninga

README.md

@@ -32,6 +32,8 @@ az login --use-device-code --tenant 07a14c4e-d88c-42f7-83b3-13af7e57ff3d
 
 > These task numbers match the Week 5 assignment chapter in your HackYourFuture Notion curriculum.
 
+> 💡 **Task 7 credentials:** the `AZURE_CREDENTIALS` JSON your CI needs in Task 7 is the same for every student in the cohort. Your teacher DMs it to you over **Slack** before the assignment is due. Ping your teacher in your cohort channel if you have not received it by the time you reach Task 7.
+
 | Task | What you do |
 |---|---|
 | 1: Choose a Pipeline | The starter `src/pipeline.py` has three functions with `raise NotImplementedError`. Implement them so the provided tests pass. |