Generate icon to font and style, & convert font style.

First, make sure you have the fontello-cli installed. For that run npm install -g fontello-cli.

$ npm install

$ npm run generateIconFont

$ npm run generateIconStyle

$ npm run updateIconConfig

Update icon in fontello and download config.json file. Then replace local config.json with new downloaded file.
Note: delete .fontello-session file after replacing config.json in local.

$ npm start

It will create font files in fonts/ directory and style files in styles/ directory. After that it will convert final style file in icon-dist/ directory.

For custom icon refer fontello wiki