Add extension

[fabaff]

Build process fails otherwise.

[...]
copying build/lib/sslstrip/URLMonitor.py -> build/bdist.linux-x86_64/wheel/sslstrip
running install_data
creating build/bdist.linux-x86_64/wheel/sslstrip-2.0.data
creating build/bdist.linux-x86_64/wheel/sslstrip-2.0.data/data
creating build/bdist.linux-x86_64/wheel/sslstrip-2.0.data/data/share
creating build/bdist.linux-x86_64/wheel/sslstrip-2.0.data/data/share/sslstrip
error: can't copy 'README': doesn't exist or not a regular file

ERROR Backend subprocess exited when trying to invoke build_wheel