doc: add how to run site (#16)

Closes #15

* feat: add how to run site

* Update README.md

Co-authored-by: Max Thirouin <git@moox.io>

Author: enieber

README.md

@@ -8,6 +8,20 @@ Website for reason-react-native
 
 Read the [contribution guidelines](https://github.com/reason-react-native/.github/blob/master/CONTRIBUTING.md) before contributing.
 
+
+## Required to run
+
+- install [nodejs](https://nodejs.org/en/)
+- install [yarn](https://yarnpkg.com/)
+
+
+## How to run site
+
+- install dependencies using yarn `yarn`
+- run build with this command `yarn build`
+- run server to test with this command `yarn start`
+
+
 ## Code of Conduct
 
 We want this community to be friendly and respectful to each other. Please read