Shorten docstring

Author: rcaneill

gsw/stability.py

@@ -47,12 +47,10 @@ def Nsquared(SA, CT, p, lat=None, axis=0):
     Returns
     -------
     N2 : array
-        Buoyancy frequency-squared at pressure midpoints, rad^2/s^2.
+        Buoyancy frequency-squared at pressure midpoints, 1/s^2.
         The shape along the pressure axis dimension is one
         less than that of the inputs.
-        The units of N2 are radians2 s-2 however in may textbooks this is
-        abbreviated to s-2 as radians does not have a unit.  To convert the
-        frequency to hertz, cycles sec-1, divide the frequency by 2π, ie N/(2π).
+        (Frequency N is in radians per second.)
     p_mid : array
         Pressure at midpoints of p, dbar.
         The array shape matches N2.