add px and python ref link

Author: ry-v1

doc/python/splom.md

@@ -289,4 +289,7 @@ fig.update_layout(title=title,
                   hovermode='closest')
 
 fig.show()
-```
+```
+#### Reference
+
+See [function reference for `px.scatter_matrix()`](https://plotly.com/python-api-reference/generated/plotly.express.scatter_matrix) or https://plotly.com/python/reference/splom/ for more information and chart attribute options!