Added SDM and sample of related precursor papers

[allenschmaltz]

These may be of interest to the audience. I added the instance-based, metric (representation) learning, interpretability, and uncertainty quantification papers, which for the reasons noted in the comments, are directly applicable to the hallucination detection task (in its various forms). The recommended approach moving forward is the SDM-based approaches in the most recent paper, "Similarity-Distance-Magnitude Universal Verification", but I think folks may be interested in the related background of the preceding two papers, which are relatively old compared to other papers in this repo. (I have other related papers, as well, but these cover the crux of the approaches.)

I didn't see an obvious ordering in the list, so I just added these directly under the header assuming you will re-arrange. (Also, obviously, feel free to not include any or all of these suggestions.)