Quick fix/suggestion - fix example script

[a-sunkari]

Just wanted to highlight an issue with the example script which can be easily fixed:

import CAD_to_OpenMC.assembly as ab

A=ab.Assembly('geometry.step')
ab.mesher_config['threads']=1
ab.mesher_config['tolerance']=1e-2
ab.mesher_config['angular_tolerance']=1e-2
A.run(h5m_filename='geometry.h5m',backend='stl2')

The line A=ab.Assembly('geometry.step') should instead be A=ab.Assembly('[geometry.step]'). Without these square brackets, the code interprets only the first letter of the file (i.e. "g") instead of the full file name, leading to errors.