improve wording

Author: vladak

docs/index.html

@@ -87,7 +87,7 @@ <h2><a name="materials">Materials</a></h2>
   as used during the lectures</a>.  They are part of the commented slides so you
   will probably not need them.
   <li>See opening slides for recommended materials for further study.
-  <li>An extensive list of recommended and not recommended materials can be
+  <li>An extensive list of recommended and not recommended C programming materials can be
   found on <a href="http://tjn.fjfi.cvut.cz/~virius/liter/litCpp.htm">Miroslav
   Virius's page.</a> Mr. Virius teaches C/C++ at the Faculty of Nuclear Sciences
   and Physical Engineering in Prague.