Add userland hello world sanity check

kernel_module/user/README.md

@@ -9,6 +9,7 @@ C programs require cross compiling, but give us more control over system calls.
 These programs can also be compiled and used on host.
 
 1.  Standalone
+    1.  [hello](hello.c)
     1.  [myinsmod](myinsmod.c)
     1.  [myrmmod](myrmmod.c)
     1.  [usermem](usermem.c)

kernel_module/user/hello.c

@@ -0,0 +1,7 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(void) {
+	puts("hello");
+	return EXIT_SUCCESS;
+}