docs: add detection area cropping section with usage instructions

Author: willuhmjs

docs/bounding.png

@@ -26,3 +26,7 @@ The configuration of the detection feature is fairly straightforward, and it is
 * **Bigger does not always mean better.**
 
 {{ read_csv('models.csv') }}
+
+## Detection Area Cropping
+![example of detection area cropping](bounding.png)
+You can specify areas for Forgetti to monitor by drawing bounding boxes on the camera stream. Simply click and drag to create a box. Forgetti will only report failures detected within these boxes. If no bounding boxes are defined, the entire camera feed will be monitored.