doc/go1.5.txt: mention bugs found by go-fuzz

I think it's worth mentioning.
But the final decision is up to you.

Change-Id: I3959132600ecc554988524ede73a7f6e8eac8353
Reviewed-on: https://go-review.googlesource.com/10551Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

doc/go1.5.txt

@@ -146,3 +146,9 @@ ARM assembly syntax has had some features removed.
 	
 Also expression evaluation now uses uint64s instead of signed integers and the
 precedence of operators is now Go-like rather than C-like.
+
+Standard library hardening
+35 bugs found by randomized testing with go-fuzz (https://github.com/dvyukov/go-fuzz)
+were fixed in fmt, archive/zip, archive/tar, encoding/gob, image/jpeg, image/png,
+image/gif, compress/flate, text/template, html/template. The fixes harden implementation
+against incorrect and malicious inputs.