math/rand: improve package documentation

Notify readers that interval notation is used.
Fixes: #26765

Change-Id: Id02a7fcffbf41699e85631badeee083f5d4b2201
Reviewed-on: https://go-review.googlesource.com/127549Reviewed-by: Rob Pike <r@golang.org>

src/math/rand/normal.go

@@ -27,9 +27,9 @@ func absInt32(i int32) uint32 {
 	return uint32(i)
 }
 
-// NormFloat64 returns a normally distributed float64 in the range
-// [-math.MaxFloat64, +math.MaxFloat64] with
-// standard normal distribution (mean = 0, stddev = 1).
+// NormFloat64 returns a normally distributed float64 in
+// the range -math.MaxFloat64 through +math.MaxFloat64 inclusive,
+// with standard normal distribution (mean = 0, stddev = 1).
 // To produce a different normal distribution, callers can
 // adjust the output using:
 //

src/math/rand/rand.go

@@ -11,6 +11,9 @@
 // The default Source is safe for concurrent use by multiple goroutines, but
 // Sources created by NewSource are not.
 //
+// Mathematical interval notation such as [0, n) is used throughout the
+// documentation for this package.
+//
 // For random numbers suitable for security-sensitive work, see the crypto/rand
 // package.
 package rand