update README

Author: sambaiz

README.md

@@ -1,13 +1,23 @@
 # lambda-npm-layer
 
-Enable `npm install` execution in Lambda function.
+Enable `npm` command execution in Lambda function.
 
 ```
 $ make build
 $ make local-run
 $ open http://localhost:3000
 ```
 
+```
+$ tree -L 2 npm-layer
+npm-layer
+├── bin
+│   ├── node
+│   └── npm -> ../nodejs/node_modules/npm/bin/npm-cli.js
+└── nodejs
+    └── node_modules
+```
+
 ## Article
 
 [Lambda上でnpm installする - sambaiz-net](https://www.sambaiz.net/article/233/)