Suggest a useful HTML snippet instead of a questionable bold tag in the documentation

At the moment, the documentation of the help macro suggests <b>bold</b> which is questionable from the point of view of semantic HTML, even though in HTML 5 this is no longer just a visual markup tag (but it still fails a test we have). Further, this example is quite bad as the HTML is actually rendered as <strong>bold</strong> in XWiki before 14.1RC1. A good example could instead be <abbr title="HyperText Markup Language">HTML</abbr> as this has no equivalent XWiki syntax.