rename init_dev_kmsg to time_boot and move doc to README

kernel_module/user/time_boot.c

@@ -0,0 +1,13 @@
+/* https://github.com/cirosantilli/linux-kernel-module-cheat#time_boot-out */
+
+#include <stdio.h>
+#include <unistd.h>
+
+int main(void) {
+    FILE *fp;
+    fp = fopen("/dev/kmsg", "w");
+	fputs(__FILE__ "\n", fp);
+	fclose(fp);
+	while (1)
+		sleep(0xFFFFFFFF);
+}