Update CONTRIBUTING

Author: cola119

CONTRIBUTING.md

@@ -1,9 +1,16 @@
-## Install
+## How to contribute to LIFF Inspector
 
-<!-- WIP -->
-<!-- ```sh
-$ git clone
+First of all, thank you so much for taking your time to contribute! We always welcome your ideas and feedback. Please feel free to make any pull requests.
+
+- File an issue in [the issue tracker](https://github.com/line/liff-inspector/issues) to report bugs and propose new features and improvements.
+- Ask a question using [the issue tracker](https://github.com/line/liff-inspector/issues).
+- Contribute your work by sending [a pull request](https://github.com/line/liff-inspector/pulls).
+
+### Setting up LIFF Inspector for development
+
+```bash
+$ git clone [email protected]:line/liff-inspector.git
 $ cd liff-inspector
 $ nvm use
-$ npm install --ws
-``` -->
+$ npm install
+```