Use a supported shape in the BeautifyIcon example (#2297)

Author: ac1982

docs/user_guide/plugins/beautify_icon.md

@@ -8,11 +8,14 @@ import folium.plugins
 
 ## BeautifyIcon
 
+Use one of the supported icon shapes: `circle`, `circle-dot`, `doughnut`,
+`rectangle-dot`, or `marker`. The default is `circle`.
+
 ```{code-cell} ipython3
 m = folium.Map([45.5, -122], zoom_start=3)
 
 icon_plane = folium.plugins.BeautifyIcon(
-    icon="plane", border_color="#b3334f", text_color="#b3334f", icon_shape="triangle"
+    icon="plane", border_color="#b3334f", text_color="#b3334f", icon_shape="circle"
 )
 
 icon_number = folium.plugins.BeautifyIcon(

folium/plugins/beautify_icon.py

@@ -14,7 +14,8 @@ class BeautifyIcon(JSCSSMixin, MacroElement):
     icon: string, default None
         the Font-Awesome icon name to use to render the marker.
     icon_shape: string, default None
-        the icon shape
+        One of "circle", "circle-dot", "doughnut", "rectangle-dot", or "marker".
+        If None, the plugin uses its default "circle" shape.
     border_width: integer, default 3
         the border width of the icon
     border_color: string with hexadecimal RGB, default '#000'