improve geo_strf_steric_height docstring

Author: DocOtak

gsw/geostrophy.py

@@ -133,7 +133,12 @@ def geo_strf_steric_height(SA, CT, p, p_ref=0, axis=0, max_dp=1.0, interp_method
     Returns
     -------
     steric_height : array
-        Dynamic height anomaly divided by the acceleration of gravity.
+        This is the integral of specific volume anomaly with respect
+        to pressure, from each pressure in p to the specified
+        reference pressure divided by the constant value of the gravitational 
+        acceleration, 9.7963 m s^-2. It is not exactly the height of an 
+        isobaric surface above a geopotential surface, but is an exact
+        geostrophic streamfunction.
 
     """
     return (