fix(docs): add missing midpoints styles docs (#1048)

Co-authored-by: Vladimir Agafonkin <agafonkin@gmail.com>

Author: adi carmel

docs/EXAMPLES.md

@@ -74,6 +74,17 @@ mapbox.Draw({
         "fill-opacity": 0.1
       }
     },
+    // polygon mid points
+    {
+    'id': 'gl-draw-polygon-midpoint',
+    'type': 'circle',
+    'filter': ['all',
+      ['==', '$type', 'Point'],
+      ['==', 'meta', 'midpoint']],
+    'paint': {
+      'circle-radius': 3,
+      'circle-color': '#fbb03b'
+    },
     // polygon outline stroke
     // This doesn't style the first edge of the polygon, which uses the line stroke styling instead
     {