doc: update wiki article to use html/template properly.

Fixes #3569.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/6116055

doc/articles/wiki/edit.html

-<h1>Editing {{.Title |html}}</h1>
+<h1>Editing {{.Title}}</h1>
 
-<form action="/save/{{.Title |html}}" method="POST">
-<div><textarea name="body" rows="20" cols="80">{{printf "%s" .Body |html}}</textarea></div>
+<form action="/save/{{.Title}}" method="POST">
+<div><textarea name="body" rows="20" cols="80">{{printf "%s" .Body}}</textarea></div>
 <div><input type="submit" value="Save"></div>
 </form>

doc/articles/wiki/index.html

@@ -359,10 +359,10 @@ First, we must add <code>html/template</code> to the list of imports:
 
 <pre>
 import (
+	<b>"html/template"</b>
 	"http"
 	"io/ioutil"
 	"os"
-	<b>"html/template"</b>
 )
 </pre>
 
@@ -397,10 +397,11 @@ Template directives are enclosed in double curly braces.
 The <code>printf "%s" .Body</code> instruction is a function call
 that outputs <code>.Body</code> as a string instead of a stream of bytes,
 the same as a call to <code>fmt.Printf</code>.
-The <code>|html</code> part of each directive pipes the value through the
-<code>html</code> formatter before outputting it, which escapes HTML
-characters (such as replacing <code>&gt;</code> with <code>&amp;gt;</code>),
-preventing user data from corrupting the form HTML. 
+The <code>html/template</code> package helps guarantee that only safe and
+correct-looking HTML is generated by template actions. For instance, it
+automatically escapes any greater than sign (<code>&gt;</code>), replacing it
+with <code>&amp;gt;</code>, to make sure user data does not corrupt the form
+HTML.
 </p>
 
 <p>

doc/articles/wiki/view.html

-<h1>{{.Title |html}}</h1>
+<h1>{{.Title}}</h1>
 
-<p>[<a href="/edit/{{.Title |html}}">edit</a>]</p>
+<p>[<a href="/edit/{{.Title}}">edit</a>]</p>
 
-<div>{{printf "%s" .Body |html}}</div>
+<div>{{printf "%s" .Body}}</div>