design: clarify why the support of the float values is a problem
design: clarify why the support of the float values is a problem

Change-Id: I3b858e61e70e7773ef32c409bf0b61cb96e89c7e
Reviewed-on: https://go-review.googlesource.com/18171
Reviewed-by: Burcu Dogan <347c19a639ce752a783b4ea325d6539ab4b4a262@google.com>

golang/proposal,golang/proposal