Mention new packages in https://texfaq.org/FAQ-underline and comparisons

[user202729]

Consider mentioning soulpos and lua-ul too.

It would also be good to have a comparison between them e.g.

• the depth of the underline is consistent unlike \underline (https://tex.stackexchange.com/questions/13377/how-can-i-underline-a-single-word-with-latex#comment583953_13382)
• lua-ul can handle arbitrary commands inside the argument
• soul doesn't support Unicode character such as Ü (https://tex.stackexchange.com/a/142359/250119)
• soulpos supports nonhomogeneous decoration (e.g. wavy line), but requires two compilation passes
• ulem doesn't support hyphenation (https://tex.stackexchange.com/a/74910/250119)

[davidcarlisle]

@user202729 any chance of a pull request?