doc/install-source.html: mention make.bash to skip tests

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/42590043

doc/install-source.html

@@ -176,6 +176,10 @@ architecture, and root directory used during the install.
 <p>
 For more information about ways to control the build, see the discussion of
 <a href="#environment">environment variables</a> below.
+<code>all.bash</code> (or <code>all.bat</code>) runs important tests for Go,
+which can take more time than simply building Go. If you do not want to run
+the test suite use <code>make.bash</code> (or <code>make.bat</code>)
+instead.
 </p>
 </div>