How do you do URLs or hyperlinks in a groff or troff document?

A question for groff/troff veterans whose knowledge extends beyond mine. Subject explains it all.

I want to have typical clickable hyperlinks in a pdf document generated by groff, but I haven't found a way of doing this so far. If you know, your help is appreciated! Email here:!

The use case is that I'm rewriting the LARBS guide (originally in R markdown) to groff so it can be easily an quickly built and updated a LARBS install (R is not installed by default and I don't want to have it and R markdown as a hard dependency just to build one document). I've had to recompile the R markdown .pdf every time I update the guide, thus causing for a pretty bloated git history, but making it recomile quickly on startup on each user's machine would be much better not just to make the git repo cleaner, but allows a quicker update in response to changes to the text source.