add lab answers

labcodes_answer/lab7_result/user/hello.c

@@ -0,0 +1,11 @@
+#include <stdio.h>
+#include <ulib.h>
+
+int
+main(void) {
+    cprintf("Hello world!!.\n");
+    cprintf("I am process %d.\n", getpid());
+    cprintf("hello pass.\n");
+    return 0;
+}
+