Clarify README and mention FOS v2

[daniel-chou]

Update README to bridge the knowledge gap between those who've "done it" and someone trying the repo for the first time:

1. Must use Python 3.8, which will discontinue support in OCT 2024. I haven't tried 3.9, but neither 3.10 nor 3.11 work.
2. Must install dvc-gs, and make sure to run the DVC commands to pull the pickles and bins
3. requirements.txt needs some updates
4. pybind11 might be needed
5. Must use gensim 3.8.3, because 4.x isn't backward compatible
6. Must use scikit-learn 1.0.2, something to do with a specific Cython version distributed with Python 3.8

On the matter of writing style, seek balance between understated vs thou-shall.