docs: add known issues section

README.md

@@ -2,7 +2,7 @@
 
 <img src="icons/icon.svg" alt="Light blue icon with white border. Shape is a pin for the current position on a map." align="right" width="128" height="128" />
 
-Replace Google Maps iFrames with OpenStreetMap
+**Replace Google Maps iFrames with OpenStreetMap**
 
 ## Capabilities
 
@@ -74,3 +74,9 @@ end
 
 mdata -->|use map data| mview([Load Leaflet Map])
 ```
+
+### Known issues
+
+- Sometimes the zoom level is completely wrong
+- Not working when a website does not use an iFrame / embed
+- Not working when iFrame uses only CIDs