docs: add private recording submission + optional Azure Blob path

"My submission" now asks for the presentation recording link with a privacy
warning (never public, never commit the .mp4), and points to the optional
Azure-native path (upload to the shared student-submissions container, share a
read-only link) documented in the Week 11 Assignment chapter.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Lasse Benninga

README.md

@@ -49,10 +49,16 @@ Fill in `week11-streamlit/metric_definitions.md`: a five-field definition (name,
 ## My submission
 
 <!-- TODO: 1) Save your Metabase dashboard into the shared "Week 11 Submissions" collection.
-     2) Paste its link below, plus screenshots or a PDF export in this repo. -->
+     2) Paste its link below, plus screenshots or a PDF export in this repo.
+     3) Paste your 5-minute presentation recording link (keep it PRIVATE). -->
 
 - Metabase dashboard (in the **Week 11 Submissions** collection): TODO
 - Screenshots / PDF export: TODO
+- Presentation recording (unlisted / shared-only, never public): TODO
+
+> ⚠️ **Keep the recording private.** It shows your screen and voice. Never make it public and never commit the `.mp4` (git history is forever). Use an unlisted Loom/YouTube or a shared-only Drive link, and check the frame for passwords, `.env` contents, or connection strings before uploading.
+
+Prefer to keep it in Azure? The assignment chapter documents an **optional advanced path**: upload the recording to the shared `student-submissions` blob container (teachers get read access, nothing is public) and share a read-only link. See "Optional (advanced): host the recording on Azure Blob Storage" in the Week 11 Assignment chapter.
 
 ## Check your score locally