More info about nodejs.

nodejs is required to build the HTML, not only to run the server locally.
Moreover, some systems (.e.g, Ubuntu) install a 'nodejs' executable,
but the building process searches for a 'node' one when building
highlights, and therefore it is required to link or alias the
real executable.

Author: fluca1978

README.md

@@ -60,6 +60,14 @@ To build the documentation web pages, simply run
 
     $ make html
 
+Please note that you will need to have [nodejs](https://nodejs.org)
+installed to produce HTML content with the above command.
+Moreover, depending on your system and installation, you could need
+to either *alias* or *link* the [nodejs](https://nodejs.org) executable
+so that you can run a command `node`. For instance:
+
+    $ ln `which nodejs` /usr/bin/node
+
 After the pages have been generated, you can view them on your local
 computer by starting the included `app.pl` program: