Update MissingReturnType.md (#3942)
Update MissingReturnType.md (#3942)

* Update MissingReturnType.md

It would be useful if these pages included the fix.

* Update MissingReturnType.md

Co-authored-by: Matthew Brown <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@muglug.com>
vimeo/psalm,vimeo/psalm