doc/go1.3.html: mention go build -i

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews, r
https://golang.org/cl/95010049
diff --git a/doc/go1.3.html b/doc/go1.3.html
index 5d5ee47..a3d8be4 100644
--- a/doc/go1.3.html
+++ b/doc/go1.3.html
@@ -169,6 +169,12 @@
 </p>
 
 <p>
+The <a href="/cmd/go/"><code>go build</code></a> subcommand
+supports a new <code>-i</code> option to install dependencies
+of the specified target, but not the target itself.
+</p>
+
+<p>
 Finally, the go command now supports packages that import Objective-C
 files (suffixed <code>.m</code>) through cgo.
 </p>