effective_go: clarified small comment

R=rsc, cw
CC=golang-dev
https://golang.org/cl/217085

doc/effective_go.html

@@ -943,7 +943,7 @@ These examples illustrate the difference between <code>new()</code> and
 
 <pre>
 var p *[]int = new([]int)       // allocates slice structure; *p == nil; rarely useful
-var v  []int = make([]int, 100) // v now refers to a new array of 100 ints
+var v  []int = make([]int, 100) // the slice v now refers to a new array of 100 ints
 
 // Unnecessarily complex:
 var p *[]int = new([]int)