added 3d surface example (#196)

* added 3d surface example

* import bug

Author: emmanuelle

python/3d-surface-plots.md

@@ -20,7 +20,7 @@ jupyter:
     name: python
     nbconvert_exporter: python
     pygments_lexer: ipython3
-    version: 3.6.7
+    version: 3.7.3
   plotly:
     description: How to make 3D-surface plots in Python
     display_as: 3d_charts
@@ -52,6 +52,31 @@ fig.update_layout(title='Mt Bruno Elevation', autosize=False,
 fig.show()
 ```
 
+### Passing x and y data to 3D Surface Plot
+
+If you do not specify `x` and `y` coordinates, integer indices are used for the `x` and `y` axis. You can also pass `x` and `y` values to `go.Surface`. 
+
+```python
+import plotly.graph_objects as go
+
+import pandas as pd
+import numpy as np
+
+# Read data from a csv
+z_data = pd.read_csv('https://raw.githubusercontent.com/plotly/datasets/master/api_docs/mt_bruno_elevation.csv')
+z = z_data.values
+sh_0, sh_1 = z.shape
+x, y = np.linspace(0, 1, sh_0), np.linspace(0, 1, sh_1)
+
+fig = go.Figure(data=[go.Surface(z=z, x=x, y=y)])
+
+fig.update_layout(title='Mt Bruno Elevation', autosize=False,
+                  width=500, height=500,
+                  margin=dict(l=65, r=50, b=65, t=90))
+
+fig.show()
+```
+
 #### Surface Plot With Contours