document the video feature

README.md

@@ -2,5 +2,23 @@
 
 
 
+### Video Feature
+Tour uses by default the logo of the distribution based on the info from `/etc/os-release`. The application comes with a feature to replace the logo with a welcome video shipped by the distribution.
 
+To enable the feature, you need to build the application with
+```bash
+meson _builddir -Dvideo_path=/absolute/path/to/the/video.mp4
+```
 
+If you're testing the application using Builder, make sure to change the `config-opts` accordinagly & give the application filesystem access so it can play the video file.
+
+Example:
+
+This needs to be added to the `gnome-tour` module
+```json
+"config-opts" : [
+    "-Dvideo_path=/home/username/to/the/video.mp4"
+]
+```
+
+along with `--filesystem=home` in `finish-args`