qemuagenttest.c: Missing documentation (Timeout)

In tests/qemuagenttest.c, the Timeout test should always be
called last. Any additional tests should come before this.
Signed-off-by: NEric Blake <eblake@redhat.com>

tests/qemuagenttest.c

@@ -605,7 +605,8 @@ mymain(void)
     DO_TEST(Shutdown);
     DO_TEST(CPU);
     DO_TEST(ArbitraryCommand);
-    DO_TEST(Timeout);
+
+    DO_TEST(Timeout); /* Timeout should always be called last */
 
     virObjectUnref(xmlopt);