[MU4 Task] Design in-app instructions for the "Find/go to" command bar

[avvvvve]

Feature description

The "Find/go to" bar (Ctrl/Cmd + F) provides no hint on how to use it. Users must look up the command syntax in the handbook to see how it works.

We could provide a quick how-to reference in a collapsible "How to use" section or in a popup.

From the handbook:

• To go to a numbered measure: enter the measure number (counting every measure, starting with 1, irrespective of pickup measures, section breaks or manual changes to measure number offsets).
• To go to a numbered page: enter the page number using the format pXX (where XX is the page number).
• To go to a numerical rehearsal mark: enter the number using the format rXX (where XX is the name of the rehearsal mark).
• To go to a rehearsal mark starting with a letter: enter the name of the rehearsal mark (the search is case insensitive).
• N.B.: It is best to avoid naming rehearsal marks with the single letters "R", "r", "P", "p", or one of these letters with an integer (e.g. "R1" or "p3"), as this can confuse the search algorithm.