Added cclib to pip requirements.txt file
Added cclib to pip requirements.txt file

`pip install -r requirements.txt` should get all the python packages you need.
nyee/RMG-Py,enochd/RMG-Py,enochd/RMG-Py,faribas/RMG-Py,chatelak/RMG-Py,nickvandewiele/RMG-Py,comocheng/RMG-Py,chatelak/RMG-Py,pierrelb/RMG-Py,nyee/RMG-Py,nickvandewiele/RMG-Py,faribas/RMG-Py,KEHANG/RMG-Py,comocheng/RMG-Py,KEHANG/RMG-Py,pierrelb/RMG-Py