title: Add Regression Plane to 3d Scatter Plot in Plotly
body: <p>I am looking to take advantage of the awesome features in Plotly but I am having a hard time figuring out how to add a regression plane to a 3d scatter plot.  Here is an example of how to get started with the 3d plot, does anyone know how to take it the next step and add the plane?</p>
  
  <pre><code>library(plotly)
  data(iris)
  
  
  iris_plot &lt;- plot_ly(my_df, 
                  x = Sepal.Length, 
                  y = Sepal.Width, 
                  z = Petal.Length, 
                  type = "scatter3d", 
                  mode = "markers")
  
  petal_lm &lt;- lm(Petal.Length ~ 0 + Sepal.Length + Sepal.Width, 
                 data = iris)
  </code></pre>