List Teacup in Related Projects

The loss of lexically scoped variables from templates burned us enough times that we wrote [teacup](https://github.com/goodeggs/teacup) based off @mark-hahn's work on [drykup](https://github.com/mark-hahn/drykup](https://github.com/mark-hahn/drykup).

Mind if I plug teacup in the related projects to attract similarly frustrated users?