Combine demo into one root directory
diff --git a/demo/build.rs b/demo/build.rs
new file mode 100644
index 0000000..a3c31b3
--- /dev/null
+++ b/demo/build.rs
@@ -0,0 +1,10 @@
+fn main() {
+    cxx_build::bridge("src/main.rs")
+        .file("src/demo.cc")
+        .flag_if_supported("-std=c++14")
+        .compile("cxxbridge-demo");
+
+    println!("cargo:rerun-if-changed=src/main.rs");
+    println!("cargo:rerun-if-changed=src/demo.cc");
+    println!("cargo:rerun-if-changed=include/demo.h");
+}