Add a vignette about customising a Workbook-object output

[matt-dray]

{a11ytables} is intentionally simple in its interface. This is to make user's lives easier and to make sure that the best practice guidance is followed.

However, there are certain legitimate edits that people might want to make to their spreadsheet that aren't provided by {a11ytables}. I can't possibly know what all these are and it would bloat the package interface to include lots of style-tweaking functionality.

Of course, it's always been possible for people to apply their own {openxlsx} styles to the Workbook-class object produced by a11ytables::generate_workbook(). For example, a user may want to colour all their sheet-titles dark green¹.

I don't think {a11ytables} should directly support this functionality if it's contained in {openxlsx} already, but I do think it's worth providing a few examples in a vignette if people feel the need to adjust the basic style of a spreadsheet created with {a11ytables}. Th vignette could also provide some warnings against making tweaks that would result in a non-accessible output.

Footnotes

1. Yeah, so this is a simple example, but not actually a very good one. Changing the title to dark green would still provide a sufficient contrast against a white background, of course, but the font style should really be set to 'default' colour so that it adjusts to the user's personal settings in their spreadsheet program (which they may have changed for their own accessibility reasons). If the user has a default of dark green as their background for whatever reason, then a dark green title would be invisible, of course. ↩