Add Description of What Things Like Webpack and Parcel Is

[mrmonteith]

Prerequisites

• I have searched for duplicate or closed feature requests
• I have read the contributing guidelines

Proposal

The first line "The official guide for how to include and bundle Bootstrap’s CSS and JavaScript in your project using Webpack." But nothing really says what Webpack is, how or why you should use it.

Motivation and context

I'm saying it would be helpful to provide that. Otherwise it sounds like here is something you can use, but no reason as to how or why. So most people would ignore it.

[mrmonteith]

An excellent example is What Is RFS? It gives an excellent description for RFS.