docs: removing stub for reach router doc (#18784)
docs: removing stub for reach router doc (#18784)

* Adding docs to reach router

* Update docs/docs/reach-router-and-gatsby.md

Co-Authored-By: Mae Capozzi <24a271a4c9cdcbea17fac39e91a6408532fa716b@gmail.com>

* Update docs/docs/reach-router-and-gatsby.md

Co-Authored-By: Mae Capozzi <24a271a4c9cdcbea17fac39e91a6408532fa716b@gmail.com>

* Update docs/docs/reach-router-and-gatsby.md

Co-Authored-By: Kyle Gill <94ae90b5a2cda186efc52272b2c47c78482de269@gmail.com>

* Tweaks to wording based on suggestions

gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby