fix(docs): link to showcase (#9385)
fix(docs): link to showcase (#9385)

* Fix: link to showcase

This URL https://github.com/gatsbyjs/gatsby/#showcase only goes to the github page of the repository and there is no corresponding tag to scroll to. However we can find on the same page a "Showcase" link which goes to the showcase on the official Gatsby website.
I believe this was the original intention behind the link.

* Change link to relative

gatsbyjs/gatsby,mingaldrichgan/gatsby,mingaldrichgan/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,mingaldrichgan/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,0x80/gatsby,gatsbyjs/gatsby,0x80/gatsby,ChristopherBiscardi/gatsby,0x80/gatsby,ChristopherBiscardi/gatsby,ChristopherBiscardi/gatsby