[docs] [issue21510] fma documentation should provide better example.

Jayanth Koushik added the comment: @Mark: I agree. And perhaps it is also worth mentioning (on an unrelated note), that the decimal fma is not based on the internal cmath fma (it could not be) and unlike the cmath fma, it is no faster than an unfused multiply-add. ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue21510> _______________________________________