Add present.sh and document LibreOffice --show flag in README

present.sh launches the slideshow directly without opening the Impress UI.
The script is gitignored as a local convenience helper.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -2,3 +2,4 @@
 __pycache__/
 photos/
 .~lock.*
+present.sh

README.md

@@ -602,3 +602,27 @@ Note: indexing time for backends 1 and 2 is dominated by CLIP inference (CPU),
 not database write speed. The in-database backend uses the manually loaded CLIP
 models in the `VECTOR` schema; their indexing time is not measured here as it
 was performed separately by the administrator.
+
+---
+
+## Presentation
+
+The presentation `Vektoren in der Datenbank.pptx` is generated by `make_presentation.py`:
+
+```bash
+python3 make_presentation.py
+```
+
+**Start the slideshow directly** (skips the LibreOffice UI):
+
+```bash
+libreoffice --impress --show "Vektoren in der Datenbank.pptx"
+```
+
+Or use the local helper script (gitignored):
+
+```bash
+./present.sh
+```
+
+Press `Esc` to exit the presentation.