docs: Add note about updating tests to dev info

Signed-off-by: Timothy Arceri <t_arceri@yahoo.com.au>

docs/devinfo.html

@@ -56,6 +56,11 @@ To add a new GL extension to Mesa you have to do at least the following.
    If the new extension adds new GL state, the functions in get.c, enable.c
    and attrib.c will most likely require new code.
 </li>
+<li>
+   The dispatch tests check_table.cpp and dispatch_sanity.cpp
+   should be updated with details about the new extensions functions. These
+   tests are run using 'make check'
+</li>
 </ul>