fix(docs): Link to instructions on adding to plugin library (#8686)
fix(docs): Link to instructions on adding to plugin library (#8686)

* How to include a plugin in the Plugin Library

* Updated after review

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