update README

Made 3 distinct steps, clarified packaging, moved running bot at end (not needed by most people), ensured correct capitations.

Diff is confusing; easier just to [read directly](https://github.com/tomByrer/libgrabber/blob/master/README.md)
> new [SemVer](http://semver.org/)

new SemVer complaint tag

> it will automatically update your package on jsDelivr

don't use your, we don't know whos package it is. Say the repo or smt

>  `packageManager` you chose in `update.json` determines where you need to update your actual package.

Spacing and I have no idea what this means