Update README.md

change here to on docs.mapcrafter.org to improve readability and follow best practices for linking to various things.

Ref:
>For example, links that either have general text such as "More" or "Click Here", or that occur multiple times on the same page, such as "Delete" or "Edit", should be avoided in favor of links that provide text specific to the target of the link.
>
> -- <cite>https://www.webaccessibility.com/best_practices.php?technology_platform_id=5
Merge pull request #96 from thorerik/patch-1

Update README.md