Create guide for using plugins which don't have npm version

[luboskmetko]

Setting up such plugins with browserify-shim can be sometimes confusing or it doesn't work. The guide should explain using browserify-shim and list these plugins together with working code snippets

Some plugins examples:

• RoyalSlider - http://dimsemenov.com/plugins/royal-slider/
• Select 2 - https://select2.github.io/
• Smint - http://www.outyear.co.uk/smint/