Updated README

Author: tamaskis

INSTALL/3D Earth and Celestial Bodies (planet3D).mltbx

@@ -5,7 +5,8 @@ Creates high-resolution renderings of the Earth and the major celestial bodies i
 ## Syntax
 
 `planet3D(planet)`\
-`planet3D(planet,opts)`
+`planet3D(planet,opts)`\
+`planet_surface = planet3D(__)`
 
 **NOTE:** Use the `background` function (see below) to set the plot background. When using `background` to set the plot background, the function call on `background` must occur *before* the function call on `planet3D`, otherwise the background will be plotted *over* the celestial body.
 
@@ -25,6 +26,8 @@ Creates high-resolution renderings of the Earth and the major celestial bodies i
    - `RotAngle` → specifies the rotation angle about the 3rd axis of the celestial body (in degrees)
    - `Units` → specifies the units the celestial body should be drawn in. Units available are `'AU'`, `'ft'`, `'km'`, `'m'`, `'mi'`, and `'nmi'`.
 
+`planet_surface = planet3D(__)` does the same as the previous two syntaxes, but also returns the `Surface` object defining the planet.
+
 **NOTE:** All fields of `opts` do NOT have to be defined; when a field is left undefined, the rest of the plot settings are set to default values. Additionally, `Color`, `LineWidth`, and `LineStyle` are only relevant when plotting the Earth's coastlines.