doc/go1.5: add nacl get_random_bytes change, pepper-39+ required

Change-Id: Ib7374dc87fa4d4ad5854155049e511a1ff51ca97
Reviewed-on: https://go-review.googlesource.com/8081Reviewed-by: Minux Ma <minux@golang.org>

doc/go1.5.txt

@@ -34,6 +34,7 @@ net/http/cgi: fix REMOTE_ADDR, REMOTE_HOST, add REMOTE_PORT (https://golang.org/
 net/smtp: add TLSConnectionState accessor (https://golang.org/cl/2151)
 os/signal: add Ignore and Reset (https://golang.org/cl/3580)
 runtime, syscall: use SYSCALL instruction on FreeBSD (Go 1.5 now requires FreeBSD 8-STABLE+) (https://golang.org/cl/3020)
+runtime, syscall: use get_random_bytes syscall for NaCl (Go 1.5 now requires NaCl SDK pepper-39 or above) (https://golang.org/cl/1755)
 strings: add Compare(x, y string) int, for symmetry with bytes.Compare (https://golang.org/cl/2828)
 syscall: Add Foreground and Pgid to SysProcAttr (https://golang.org/cl/5130)
 syscall: add missing Syscall9 for darwin/amd64 (https://golang.org/cl/6555)