Update get_light_curve docstring (#235)

To clarify that the phrase "The radius of the transiting body in the same units as ``r_star``" does not mean "The radius of the transiting body in units of ``r_star``".

src/exoplanet/light_curves/limb_dark.py

@@ -128,7 +128,9 @@ def get_light_curve(
                 ``r_star``. This should have a shape that is consistent with
                 the coordinates returned by ``orbit``. In general, this means
                 that it should probably be a scalar or a vector with one entry
-                for each body in ``orbit``.
+                for each body in ``orbit``. Note that this is a different
+                quantity than the planet-to-star radius ratio; do not confuse
+                the two!
             t (tensor): The times where the light curve should be evaluated.
             texp (Optional[tensor]): The exposure time of each observation.
                 This can be a scalar or a tensor with the same shape as ``t``.