code review 8248044: doc: use the already defined GOPATH in PATH

doc/code.html

 <!--{
 "Title": "How to Write Go Code"
 }-->
 
 <h2 id="Introduction">Introduction</h2>
 
 <p>
 This document demonstrates the development of a simple Go package and
 introduces the <a href="/cmd/go/">go tool</a>, the standard way to fetch,
 build, and install Go packages and commands.
@@ skipping 107 matching lines @@
 $ <b>mkdir $HOME/go</b>
 $ <b>export GOPATH=$HOME/go</b>
 </pre>
 
 <p>
 For convenience, add the workspace's <code>bin</code> subdirectory
 to your <code>PATH</code>:
 </p>
 
 <pre>
-$ <b>export PATH=$PATH:$HOME/go/bin</b>
+$ <b>export PATH=$PATH:$GOPATH/bin</b>

[ioe, 2013/04/05 07:38:11]

This will only work in the example. But will mysteriously break, if the user starts adding more entries to the GOPATH. Esp. since go writes only to the FIRST component of it and export PATH=$PATH:$GOPATH/bin will only add the binary location of the LAST component to the path. The user will not see his just compiled binaries. So please remove this optimization. 

 </pre>
 
 
 <h3 id="PackagePaths">Package paths</h3>
 
 <p>
 The packages from the standard library are given short paths such as
 <code>"fmt"</code> and <code>"net/http"</code>.
 For your own packages, you must choose a base path that is unlikely to
 collide with future additions to the standard library or other external
@@ skipping 450 matching lines @@
 
 <p>
 Take <a href="http://tour.golang.org/">A Tour of Go</a> to learn the language
 proper.
 </p>
 
 <p>
 Visit the <a href="/doc/#articles">documentation page</a> for a set of in-depth
 articles about the Go language and its libraries and tools.
 </p>