doc: go1.6.txt: -msan option for cmd/{go,compile,link}

Change-Id: I8b41de496e4b58214b98267b529f3525ff6d9745
Reviewed-on: https://go-review.googlesource.com/16171Reviewed-by: Ian Lance Taylor <iant@golang.org>

doc/go1.6.txt

@@ -2,6 +2,9 @@ Tools:
 
 cmd/go: vendoring enabled by default (https://golang.org/cl/13967/)
 cmd/go: flags for tests must precede package name if present; also makes it easier to pass flags to test binaries (https://golang.org/cl/14826)
+cmd/go: add -msan option (https://golang.org/cl/16169)
+cmd/compile: add -msan option (https://golang.org/cl/16160)
+cmd/link: add -msan option (https://golang.org/cl/16161)
 
 Ports: