My wife and I want to name our baby Ruud. Would we need to use two dots over the u so that people know how to pronounce it or is it fine the way it is?
The letter sequence "UU" does not occur in English spelling, and there are no guides as to how to pronounce it. Most English speakers will pronounce a name spelled Ruud as
This is unavoidable in Anglophone areas. However, even worse is a name with any diacritics, especially one as variable as a diaresis (umlaut) mark. English does not use any of them and most keyboards don't allow their use, so it would become optional in most cases.
Further, while words like coöperate can indicate that a double vowel letter combination has a special pronunciation, it doesn't indicate what that pronunciation is.
In the case of a potential Ruüd, the only likely result would be that one of the U's would be pronounced /u/ and the other as /ə/, like "Roo-udd" /ruəd/ or "Ruh-ood" /rəud/. And anyone who knows German is likely to mistake it for a U umlaut, a sound which does not exist in English.
All in all, Ruud is not a name that's well adapted to Anglophone countries.
I think some of the answers you have received are slightly unkind. I suspect you may be a person of Dutch or German origin. If so, why not give your child a name in his ancestral language? Seems a perfectly natural thing to do in my view. As to whether to add the two dots, if you live in the UK I would say add them. I can't speak for other English-speaking countries. Your little boy should grow up enjoying using his two dots and early learn to explain to people why they are important. Most educated people in Britain, teachers etc would encourage him to employ his dots with pride.