website improvements

doc/tools.txt

@@ -4,6 +4,10 @@ Tools available with Nim
 
 The standard distribution ships with the following tools:
 
+- | `Documentation generator <docs/docgen.html>`_
+  | The builtin document generator ``nim doc2`` generates HTML documentation
+    from ``.nim`` source files.
+
 - | `Nimsuggest for IDE support <nimsuggest.html>`_
   | Through the ``nimsuggest`` tool, any IDE can query a ``.nim`` source file
     and obtain useful information like definition of symbols or suggestions for