Change "description" to clarify relationship with mathlib version

[holtzermann17]

What is the relationship to the version of tidy in mathlib? Because the build is failing here, I am assuming this version of tidy is deprecated; however, since there are relatively recent commits, maybe I am wrong and development is still taking place here. Anyway it would be great if the documentation in the README and description visible at https://github.com/semorrison/lean-tidy explains these things.

[kim-em]

Thanks, I’ve added a note at the top of the README. There’s nothing interesting here anymore.