Documenting output format

Hi, thanks for the interesting work!
I was reusing the results, and it took quite some time to understand the format. Could you please add some description of the files to the README? I gathered some notes myself (below), so maybe just posting them would be useful for others.

The only part I'm still puzzled about is the `title_citation_scores.json` file. Based on the name and the code, I assume that it shows only scientific concepts, present in titles. However, if we take 100'th element from title_citation_scores.json, it will be 'elastic weight consolidation', the top article is *20e9d860d95531772987f0e34043f543a1953b92*, arxiv id [1612.00796](https://arxiv.org/abs/1612.00796). You can see the name is "Overcoming catastrophic forgetting in neural networks", and 'elastic weight consolidation' is present only in the body. And, indeed, when checking `title_nps.json` for all articles from the 100'th cluster, it finds only one, *042be44eb9b09bc5219d3d86a4052d019ddaf390* ([1712.03847](https://arxiv.org/abs/1712.03847)). So is it right, that the `title_citation_scores.json` contains the full body citation scores?

The code to check it is:

```python
import json
with open("./title_nps.json") as f:
title_nps = json.load(f)

with open("./title_citation_scores.json") as f:
title_citation_scores = json.load(f)

title_citation_scores[100]

[title_nps[k] for k in title_citation_scores[100][0] if k in title_nps]
```

---
My description of the files:
- `body_nps.json` is a dictionary of noun phrases, which stores ids of papers that mention them
- `abstract_nps.json` and `title_nps.json` have the same info, but extracted from abstracts / titles correspondingly
- `arxiv_to_s2_mapping.json` allows to get arxiv ids from s2 ids, which are stored in `body_nps.json`
- `normalization.json` has all possible variants for each of the noun phrases
- `s2_id_to_citing_ids.json` has info on what papers cited the given one
- `s2_id_to_references.json` has the list of reference ids per paper
- `title_citation_scores.json` is a list of scientific concepts and info on them in the following format:
- `[0]` list of noun phrases, belonging to the concept
- `[1]` maximal score of the concept across all papers
- `[2]` table of info about papers that use this concept, sorted by score descending. Rows have:
- S2 paper id
- number of sampled papers that cite this one and have the same concept (`term_occurrences`)
- number of papers that have the same concept (`term_citations`)
- total score (`log(term_citations + 1) * (term_citations / term_occurrences)`)
- `title_cnlc_scores.json` and `title_loor_scores.json` are the entities and scores, obtained with other methods (`cnlc` and `loor`)