Update readme to tell users how to add waybackurl in the path variable

[sickwiz]

Currently, it is not mentioned how to add waybackurl in the path variable and hence people may face difficulty in running waybackurl inside any directory. We just need to update the readme to include wayback path variable in /etc/profile.

One just needs to add export PATH=$PATH:go/bin/waybackurls in /etc/profile.

I would like to add this in the readme. Please allow me to do so.