Update quick_guide_maxwell.rst

[dougoldenburg]

To simplify: let's present only fields in matter and also order them so that they are: Faraday Ampere-Maxwell Gauss (magnetic) Gauss (electric)

[lheagy]

@dccowan: can you touch-base with @dougoldenburg if you have questions on the intended changes here?

[dccowan]

• Redundant eqs in a vacuum have been removed.
• Improved description of variables for each set of maxwell's equations.
• Found and fixed typos and grammatical issues.
• Added necessary hyperlinks and citations.