Move --channel conda-forge argument in conda create command

Tried following the README instructions, but got an error:

$ conda create -n libcomcat python=3.6 --channel conda-forge numpy obspy pandas xlrd xlwt openpyxl
usage: conda [-h] [-V] command ...
conda: error: unrecognized arguments: numpy obspy pandas xlrd xlwt openpyxl

Swapping the python=3.6 and --channel conda-forge arguments works as expected.