Document the embedded documentation format.

src/vmod_example.vcc

 $Module example 3 Example VMOD
+This is the embedded documentation for the example VMOD. It should
+mention what the vmod is intended to do.
+
+It can span multiple lines and is written in RST format.
+You can even have links and lists in here:
+
+* https://github.com/varnish/libvmod-example/
+* https://www.varnish-cache.org/
+
+
 $Function STRING hello(STRING)
+
+The different functions provided by the VMOD should also have their own
+embedded documentation. This section is for the hello() function.