Escape command line tags in example

Since the code example is enclosed in the HTML tags <pre>, the command line
comment tag has to be escaped.

README.md

@@ -85,7 +85,7 @@ run a 'hello world' example. Your first step in bash should be no exception.
 Open a bash shell and type everything after the `$` sign and hit return.
 The shell should greet you and everybody else in the world as shown in
 this example.
-<!-- console_output -->
+&lt;!-- console_output --&gt;
 ```bash
 $ echo "Hello World!"
 Hello World!