godoc/vfs: reorder comment paras to display the correct one

This is a fixup for golang.org/cl/130796.

Change-Id: If151325738b59ab61a7b456a140d3bc8dff57b9c
Reviewed-on: https://go-review.googlesource.com/131315
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

godoc/vfs/os.go

@@ -14,12 +14,12 @@ import (
 	"runtime"
 )
 
+// We expose a new variable because otherwise we need to copy the findGOROOT logic again
+// from cmd/godoc which is already copied twice from the standard library.
+
 // GOROOT returns the GOROOT path under which the godoc binary is running.
 // It is needed to check whether a filesystem root is under GOROOT or not.
 // This is set from cmd/godoc/main.go
-
-// We expose a new variable because otherwise we need to copy the findGOROOT logic again
-// from cmd/godoc which is already copied twice from the standard library.
 var GOROOT = runtime.GOROOT()
 
 // OS returns an implementation of FileSystem reading from the