[Domain-Mapping] GitHub Tutorial to update legacy plugins

Now that we have to go to GitHub to get critical updates for legacy plugins, I request the Blog write an article showing step by step how to do that.

I have a GitHub account and cloned the domain-mapping project. I am trying to follow the READMW.md file. Actually this one doesn't seem to complex but I am also using events_and_bookings which required me to install python but I got a lot of errors.