Dataset fod documentation issues

[JoFAM]

• [ ] The dataset fod needs either a reference to an article where it comes from or another mention of its origin (own research, simulated, grabbed from database X at date Y, ...)
• [x] The dataset documentation best goes in its own file for easy maintenance. This is changed in commit https://github.com/JoFAM/nardl/commit/f3bb6681ff7976894ce682268d01bbcac327aecd
• [x] The layout of the variable explanation is messed up (used \itemize with two inputs for \item. If you want to use that construct, you need \describe instead of \itemize). This is changed in commit https://github.com/JoFAM/nardl/commit/f3bb6681ff7976894ce682268d01bbcac327aecd

[JoFAM]

@zedtaha The dataset fod still needs some indication of its origin.