diff --git a/README.md b/README.md
new file mode 100644
index 0000000..983e3a7
--- /dev/null
+++ b/README.md
@@ -0,0 +1,17 @@
+# Intro. to OS HW1
+
+## Docker Compose usage
+
+Install docker and docker-compose if not installed.
+
+1. Change uid / gid to yours in `Dockerfile` and `docker-compose.yaml`.
+2. Run `docker compose build` to build Docker image.
+3. Run `docker compose run test` to launch testing environment.
+
+## Makefile
+
+First, `cd` into `code` directory.
+
+- `make clean` to clean previous build.
+- `make` to build.
+- `make run` to run tests.
diff --git a/code/userprog/ksyscall.h b/code/userprog/ksyscall.h
index bf1b9f3..27fc524 100644
--- a/code/userprog/ksyscall.h
+++ b/code/userprog/ksyscall.h
@@ -37,7 +37,7 @@ int SysCreate(char *filename)
 }
 
 void SysPrintInt(int value) {
-  static char zero[2] = "0";
+  static char zero[3] = "0\n";
 
   if (value == 0) {
     kernel->synchConsoleOut->PutString(zero);