content: make description about rand.Intn less ambiguous

Technically rand.Intn will always return the same sequence of
numbers, however in this context, re-running the example will
always produce the same value.

Fixes golang/go#12370

Change-Id: Iea87a4b1b0db1a919a35b00d0d4af497fafd1319
Reviewed-on: https://go-review.googlesource.com/15555
Reviewed-by: Andrew Gerrand <adg@golang.org>

content/basics.article

@@ -15,7 +15,8 @@ This program is using the packages with import paths `"fmt"` and `"math/rand"`.
 By convention, the package name is the same as the last element of the import path. For instance, the `"math/rand"` package comprises files that begin with the statement `package`rand`.
 
 #appengine: *Note:* the environment in which these programs are executed is
-#appengine: deterministic, so `rand.Intn` will always return the same number.
+#appengine: deterministic, so each time you run the example program
+#appengine: `rand.Intn` will return the same number.
 #appengine:
 #appengine: (To see a different number, seed the number generator; see [[http://golang.org/pkg/math/rand/#Seed][`rand.Seed`]].)