Add not about the CK_FORK env variable

test/test_runner.c

@@ -91,6 +91,8 @@ main (int argc, char *argv[])
     if (xml_output) 
         srunner_set_xml(sr, "result.xml");
 
+    //set the environment variable CK_FORK=no which means don't fork().
+    //anything else means to fork()
     srunner_set_fork_status(sr, CK_FORK_GETENV);