add README to lib_dev

Author: cometkim

lib_dev/README.md

@@ -0,0 +1,19 @@
+# Libraries for development
+
+This is a place for development purposes libraries.
+
+You can use modules here by `#dev/*`
+
+e.g. in `scripts` or `tests`:
+
+```js
+import { setup } from '#dev/process';
+
+const { execBuild } = setup(import.meta.url);
+
+// Execute ReScript in the current file location.
+await execBuild({ stdio: "inherit" });
+```
+
+> [!IMPORTANT]  
+> DO NOT USE this modules in the compiler artifacts.