docs: fix /know/known/ typo

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

docs/about.html

@@ -50,7 +50,7 @@ cross-compilation process.</p>
   toolchain</li>
 
   <li>Has a <b>simple structure</b> that makes it easy to understand
-  and extend. It relies only on the well-know Makefile language.</li>
+  and extend. It relies only on the well-known Makefile language.</li>
 
 </ul>