I used a zip file for the 40k mod.
For Rosigma, a zip file will probably not work, the mod is quite a mess, so you will need to extract the mod (and delete or move away the zip file).
If you can't see the mod, it's likely one of two things:
1. you didn't restart openxcom (needs to be completely killed and started new)
2. the structure of the zip file is wrong (test on the PC first to be sure, don't forget to move the extracted mod away first)