Reduce readme size

[cmann1]

This is pretty minor and not directly related to the package, but the repository page is unusable for maybe 10-30 seconds every time I open the page because of the huge amount of content in the readme.

Maybe this could just have an overview and link to a secondary readme with the full documentation?

[TylerTemp]

Well, similar to core-js#1053

ATM I'd suggest to use saintsfield.comes.today instead. I'm kinda lazy to migrate this page. Will consider about it later.

[cmann1]

Oh yeah I do already use that thanks.

It's not really about the documentation, more about visiting the repository, e.g. to check an issue etc.
Which is why I said it's very minor.