panchoop

As suggested in [this issue](https://github.com/inducer/pyopencl/issues/506#issuecomment-892134405), a warning was added both in the code and in the documentation.

Array.concatenate fails for axis!= 0

1

The function only works for axis = 0. To replicate: ``` import pyopencl as cl platform = cl.get_platforms()[0] device = platform.get_devices()[0] context = cl.create_some_context([device]) queue = cl.CommandQueue(context) a = np.random.rand(2,2)...