Add an explanation about cirq-ft's status to its PyPI page

[mhucka]

cirq-ft is not a thing anymore, but it still exists on PyPI, and there's no pointer to Qualtran or other note about its status. We should do something about that. At minimum, there should be a note about its status, but perhaps it should be hidden or removed altogether.

[mhucka]

Clarification added for anyone else who might be reading this: this issue cannot be solved by editing any file in the Cirq repo. The description where the notice needs to be put is on PyPI.