Document map rotation select entity in README

Add documentation for the per-map rotation select entity.

Explains:
- How to rotate maps (0/90/180/270)
- Where to find the rotation select entity
- That calibration points are rotated as well
- That no reload is required

Also clarifies usage with Xiaomi Vacuum Map Card.

Author: TheHangMan97

README.md

@@ -26,6 +26,26 @@ map_source:
 calibration_source:
   camera: true
 ```
+### Map rotation (new)
+
+If your map is displayed sideways or upside down, you can rotate the map directly in Home Assistant.
+
+This integration provides a **Select entity per map** to control rotation:
+- `select.<...>_rotation`
+- Options: `No rotation`, `Rotate 90°`, `Rotate 180°`, `Rotate 270°` (labels depend on your HA language)
+
+This rotates **both**:
+- the map image
+- and the calibration points used by the Xiaomi Vacuum Map Card  
+  (so rooms/zones and interactions stay aligned after rotation)
+
+**How to use**
+1. Go to **Settings → Devices & services → Roborock Custom Map**
+2. Open the device/entities list
+3. Find the `… rotation` select entity for your map and choose the correct rotation
+
+No reload is required; the map updates immediately.
+
 6. You can hit Edit on the card and then Generate Room Configs to allow for cleaning of rooms. It might generate extra keys, so check the yaml and make sure there are no extra 'predefined_sections'
 
 ### Installation