Update projects.mdx (#1248)

Added url to my GatsbyJS site that depends alot on MDX.

Author: nikobenho

docs/projects.mdx

@@ -21,6 +21,7 @@
 - [Compositor][]
 - [Prisma][]
 - [Max Stoiber’s Blog][mxstbr]
+- [SmartRate][smrtrt]
 
 ## Other related links
 
@@ -37,6 +38,7 @@
 [compositor]: https://compositor.io
 [prisma]: https://www.prisma.io/docs
 [mxstbr]: https://mxstbr.com
+[smrtrt]: https://www.smartrate.se
 [awesome-mdx]: https://github.com/transitive-bullshit/awesome-mdx
 [spectacle-boilerplate-mdx]: https://github.com/FormidableLabs/spectacle-boilerplate-mdx
 [charge]: https://charge.js.org