math/big: update comment in the implementation of FloatPrec

Follow-up on CL 539299: missed to incorporate the updated
comment per feedback on that CL.

For #50489.

Change-Id: Ib035400038b1d11532f62055b5cdb382ab75654c
Reviewed-on: https://go-review.googlesource.com/c/go/+/542115
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

Author: griesemer

src/math/big/ratconv.go

@@ -403,8 +403,8 @@ func (x *Rat) FloatPrec() (n int, exact bool) {
 	//     n = max(p2, p5)
 	//     exact = q == 1
 	//
-	// See https://en.wikipedia.org/wiki/Repeating_decimal for
-	// details.
+	// For details see:
+	// https://en.wikipedia.org/wiki/Repeating_decimal#Reciprocals_of_integers_not_coprime_to_10
 	d := x.Denom().abs // d >= 1
 
 	// Determine p2 by counting factors of 2.