How can I make a geany .tags file for a C++ library?

I would like to have auto-completion on the geany text editor (no, it's not an IDE) and for that you use .tags files. There's a plugin that creates .tags files for your programs, but I need to make one for an external C++ library (SFML, more specifically). The goal is to have geany display all the possible classes when I type "sf::" and show the methods of said classes when I type those. This would be a huge deal because I could learn SFML much faster this way, without having to search things so much. Thanks.