Add README to JavaScript.

javascript/README.md

+# Using
+
+## Building and development
+Refer to the root README to set up building and development of the libs.  
+
+## Code quality
+Project uses ESLint to maintain code quality. Setup instructions: 
+
+#### VScode
+- Install [ESLint](https://marketplace.visualstudio.com/items?itemName=dbaeumer.vscode-eslint) plugin
+
+#### IDEA 
+- Enable ESLint in `Preferences -> Languages and frameworks -> JavaScript -> Code Quality Tools`
+
+