Update Run Steps

[JcMinarro]

Update Run Steps for users that didn't install dependencies previously.

If you try to run the project without installing the dependencies an error is shown to you, something like:

$ npm run dev
> mastodon-followgraph@0.1.0 dev
> next dev

/tmp/dev-12b79e87.sh: 1: next: not found

[gabipurcaru]

looks good, thanks for the contribution. This is actually the default next.js readme so you might want to fix it upstream for better impact :)