Can we simplify the onboarding via helloworld.rb

[alterisian]

I really liked how it was relatively simple for people to add their twitter handle to the platform.
Over time I've ended up sharing the particular line that people need to add to.
i.e. https://github.com/alterisian/helloworld/blob/main/helloworld.rb#L247
This kinda works, but would be better if it was just obvious!

Ideas:

• we could just move the list of people to the top of the file?
• we could refactor, so the helloworld.rb 's responsibility is to add people to the platform, and move all the other code into platform.rb (new class).