Add a link to friends page to index.html

Author: brson

en-US/index.html

@@ -11,7 +11,7 @@
           prevents segfaults,
           and guarantees thread safety.
           <br/>
-          <a href="https://doc.rust-lang.org/book/README.html">Show me!</a>
+          <b><a href="friends.html">See who's using Rust.</a></b>
         </p>
       </div>
       <div class="col-md-4 install-box">