Update GeoJson doc-string about __geo_interface__ (#1425)

* Update GeoJson doc-string

* Remove trailing whitespaces

Author: kai-tub

folium/features.py

@@ -324,6 +324,9 @@ class GeoJson(Layer):
         * If dict, then data will be converted to JSON and embedded
         in the JavaScript.
         * If str, then data will be passed to the JavaScript as-is.
+        * If `__geo_interface__` is available, the `__geo_interface__`
+        dictionary will be serialized to JSON and
+        reprojected if `to_crs` is available.
     style_function: function, default None
         Function mapping a GeoJson Feature to a style dict.
     highlight_function: function, default None