Add installation instructions to the README

[KirstieJane]

@RaoOfPhysics has already added a few installation instructions in #3, and I'm just running through them now to check they work (and to be able to run the MVP locally!)

I think there are probably a few things missing - do you need to have BeakerBrowser or Dat installed already?

It looks like I need npm too?

If anyone has time to comment here, I'm super happy to actually do the additions to the README (I just need help knowing what to do!)

Thank you ✨

[RaoOfPhysics]

Also happy to help! Just tag me. :)