docs: add column_stack to ndarray-for-numpy-users guide

Closes #650

Author: chiliec

src/doc/ndarray_for_numpy_users/mod.rs

@@ -536,6 +536,7 @@
 //! `a[:5, 2] = b` | [`a.slice_mut(s![..5, 2]).assign(&b)`][.assign()] | copy the data from array `b` into part of array `a`
 //! `np.concatenate((a,b), axis=1)` | [`concatenate![Axis(1), a, b]`][concatenate!] or [`concatenate(Axis(1), &[a.view(), b.view()])`][concatenate()] | concatenate arrays `a` and `b` along axis 1
 //! `np.stack((a,b), axis=1)` | [`stack![Axis(1), a, b]`][stack!] or [`stack(Axis(1), vec![a.view(), b.view()])`][stack()] | stack arrays `a` and `b` along axis 1
+//! `np.column_stack((a,b))` or `np.c_[a,b]` | [`stack![Axis(1), a, b]`][stack!] or [`stack(Axis(1), &[a.view(), b.view()])`][stack()] | stack 1-D arrays `a` and `b` as columns into a 2-D array
 //! `a[:,np.newaxis]` or `np.expand_dims(a, axis=1)` | [`a.slice(s![.., NewAxis])`][.slice()] or [`a.insert_axis(Axis(1))`][.insert_axis()] | create an view of 1-D array `a`, inserting a new axis 1
 //! `a.transpose()` or `a.T` | [`a.t()`][.t()] or [`a.reversed_axes()`][.reversed_axes()] | transpose of array `a` (view for `.t()` or by-move for `.reversed_axes()`)
 //! `np.diag(a)` | [`a.diag()`][.diag()] | view the diagonal of `a`