Hello demo program

user/hello.c

@@ -0,0 +1,13 @@
+#include "kernel/types.h"
+#include "kernel/stat.h"
+#include "user/user.h"
+
+int
+main(int argc, char *argv[])
+{
+  char hello[] = "Hello XV6!\n";
+
+  write(1, hello, sizeof(hello));
+
+  exit(0);
+}