install.html: ed needs to be installed too

Fixes #14.

R=r
https://golang.org/cl/152052

Author: rsc

doc/install.html

@@ -154,13 +154,13 @@ <h2>Fetch the repository</h2>
 <h2>Install Go</h2>
 
 <p>The Go tool chain is written in C.  To build it, you need
-to have  GCC, the standard C libraries, and the parser generator Bison
+to have GCC, the standard C libraries, the parser generator Bison, and the text editor ed
 installed.  On OS X, they can be installed as part of <a href="http://developer.apple.com/TOOLS/Xcode/">Xcode</a>.
 On Linux, 
 </p>
 
 <pre>
-$ sudo apt-get install bison gcc libc6-dev
+$ sudo apt-get install bison gcc libc6-dev ed
 </pre>
 
 <p>