Add instance for `text-containers

[chshersh]

This package:

• https://hackage.haskell.org/package/text-containers-0.1.0.0

[kahlil29]

I'd like to pick this up. Is there any other previously added package that has been added to this repo that I can use as reference?

[chshersh]

@kahlil29 Yes, the implementation should look pretty much like for containers-int-strict. I think we settled with the implementation of the Map signature for IntMap so the implementation can be take as the example.