doc: update installation instructions
Clarify that GOROOT should only be set when using a custom install path.
Remove NetBSD from binary install page (we don't provide binaries).
Remove "What's next" links from installation instructions.
Emphasize "How to Write Go Code" page.
Fixes #6613.
R=golang-dev, r
CC=golang-dev
https://golang.org/cl/28700043
diff --git a/doc/install-source.html b/doc/install-source.html
index 59d984f..b99360c 100644
--- a/doc/install-source.html
+++ b/doc/install-source.html
@@ -216,10 +216,23 @@
<h2 id="gopath">Set up your work environment</h2>
<p>
-The document <a href="/doc/code.html">How to Write Go Code</a> explains how to
-set up a work environment in which to build and test Go code.
+You're almost done.
+You just need to do a little more setup.
</p>
+<p>
+<a href="/doc/code.html" class="download" id="start">
+<span class="big">How to Write Go Code</span>
+<span class="desc">Learn how to set up and use the Go tools</span>
+</a>
+</p>
+
+<p>
+The <a href="/doc/code.html">How to Write Go Code</a> document
+provides <b>essential setup instructions</b> for using the Go tools.
+</p>
+
+
<h2 id="tools">Install additional tools</h2>
<p>
