codelab/index.html: a few typos.

R=adg
CC=golang-dev
https://golang.org/cl/993042

doc/codelab/wiki/index.html

@@ -180,7 +180,7 @@ func loadPage(title string) (*page, os.Error) {
 
 <p>
 Callers of this function can now check the second parameter; if it is
-<code>nil</code> then it has succesfully loaded a page. If not, it will be an
+<code>nil</code> then it has successfully loaded a page. If not, it will be an
 <code>os.Error</code> that can be handled by the caller (see the <a
 href="http://golang.org/pkg/os/#Error">os package documentation</a> for 
 details).
@@ -222,7 +222,7 @@ This is a sample page.
 <p>
 (The <code>8g</code> and <code>8l</code> commands are applicable to
 <code>GOARCH=386</code>. If you're on an <code>amd64</code> system,
-subtitute 6's for the 8's.)
+substitute 6's for the 8's.)
 </p>
 
 <p>
@@ -452,7 +452,7 @@ import (
 </pre>
 
 <p>
-Let's create a template file containg the HTML form. 
+Let's create a template file containing the HTML form. 
 Open a new file named <code>edit.html</code>, and add the following lines:
 </p>