Added musical example of double sharps and flats #3855

[byoojh]

Added a section in the guide under the sharps and flat to describe use cases of double sharps and flats, along with some well known musical examples.

[pikurasa]

I'm assuming this is ready for review, so I'm checking it out.

[pikurasa]

It's going well so far. Two comments:

1. Accidentals

In addition to using the "accidental override", I think you should add examples of selecting those accidentals from the pie menu as follows:

2. Left/right

In the text, it refers to examples on the left and right. However, they display for me above and below. Perhaps just refer to them as first and second example, or, if you can, add captions underneath and refer to them as "the example by Liszt" and "the example by Bartok".