What he gave you is xml info. To find the XML file, open up the orbis file from where you have it stored (should be under mods under your Beyond the Sword install). Once you have opened that file, go to assets>XML>Units and then open up CIV4PromotionsInfos.
Once you've done that, you can just add the code that he gave you in at the end, then start orbis again (note, don't do this while orbis is running). If orbis starts up just fine, then it worked. If it gave you XML exceptions when launching, you did something wrong. There are already alot of similar promotions already there, just look at them and you should see how to do this properly. You can do this all with notepad. I would recommend starting a new game to test and see if it works before going back to your old one however. I would also recommend making a copy of your orbis install before doing this, even if you don't really need it, mostly because I'm a paranoid programmer.
-Colin