add docs for chip widget

[tabacitu]

This PR adds docs for the chip widget introduced in Laravel-Backpack/CRUD#5815 and with demo examples in Laravel-Backpack/demo#701

Documented:

• what is a chip
• how to use the crud::chips.general chip
• how to use chips as widgets
• how to use chips as columns
• how to use chips outside CrudControllers
• how to create your own chip

Todo:

• add images
• polish text & layout

[tabacitu]

While trying to document this feature, I've realised that... it's difficult to document it, because it's unlike any other features we have:

• it's not a Component, so we can't add it to Components
• it's not a standard CRUD feature, so we can't document it in fields or columns

Currently I think we have the following options:

• (A) we can turn it into a Component - and maybe call it Datachip; but realistically the PHP Class won't do anything; and I do NOT want this to take its info from a controller, that is overkill and would make it more difficult to customize than I intend it to;
• (B) we can keep it a Blade view - and document it in a separate page under the Show & List operations; we basically create a new TYPE of blade file (chips), which comes with one built-in file... and a way to create your own;

From the above... I think I like Option B best. So I'm going to do that.