Doc: define h2d.Tile for Font

doc/ref.html

@@ -280,6 +280,12 @@ The following blend mode values are available :
 </p>
     
 <h2>H2D Font</h2>
+
+<p>
+    Font use <code>h2d.Tile</code> to storage characters.
+</p>
+    
+<p>We can initialize <code>h2d.Font</code> from a bitmap</p>
     
 <p>
     To display text in H2D you must have a bitmap font ressource. It's easy to build this ressource width <a href="https://github.com/andryblack/fontbuilder/downloads">FontBuilder</a>.