Add documentation about where

Author: martinRenou

docs/source/xarray.rst

@@ -126,6 +126,7 @@ where ``condition`` is falsy, and it does not evaluate ``b`` where ``condition``
 | Python 3 - xarray | C++ 14 - xframe |
 +===============================================+===============================================+
 | ``xr.where(a > 5, a, b)`` | ``xf::where(a > 5, a, b)`` |
+| ``xr.where(a > 5, 100, a)`` | ``xf::where(a > 5, 100, a)`` |
 +-----------------------------------------------+-----------------------------------------------+
 | ``np.any(a)`` | ``xf::any(a)`` |
 +-----------------------------------------------+-----------------------------------------------+
@@ -251,4 +252,3 @@ xframe universal functions are provided for a large set number of mathematical f
 +-----------------------------------------------+-----------------------------------------------+
 | ``scipy.special.gammaln(a)`` | ``xf::lgamma(a)`` |
 +-----------------------------------------------+-----------------------------------------------+
-