Update README.md

README.md

@@ -43,7 +43,7 @@ tags:
 
 4,062,423 chess puzzles, rated and tagged. See them in action on [Lichess](https://lichess.org/training/themes). 
 
-Generating these chess puzzles took more than **50 years of CPU time**. We went through **300,000,000 analyzed games** from the Lichess database, and re-analyzed interesting positions with Stockfish 12/13/14/15 NNUE at 40 meganodes. The resulting puzzles were then [automatically tagged](https://github.com/ornicar/lichess-puzzler/tree/master/tagger). To determine the rating, each attempt to solve is considered as a Glicko2 rated game between the player and the puzzle. Finally, player votes refine the tags and define popularity.
+Generating these chess puzzles took more than **50 years of CPU time**. We went through **300,000,000 analyzed games** from the Lichess database, and re-analyzed interesting positions with Stockfish 12/13/14/15 NNUE at 40 meganodes. The resulting puzzles were then [automatically tagged](https://github.com/ornicar/lichess-puzzler/tree/master/tagger). To determine the rating, each attempt to solve is considered as a Glicko-2 rated game between the player and the puzzle. Finally, player votes refine the tags and define popularity.
 
 
 ## Dataset Usage
@@ -77,13 +77,18 @@ One row of the dataset looks like this:
 
 Every row of the dataset contains the following fields:
 
-- `PuzzleId`:
-- `FEN`:
-- `Moves`:
-- `Rating`:
-- `RatingDeviation`:
-- `Popularity`:
-- `NbPlays`:
-- `Themes`:
-- `GameUrl`:
-- `OpeningTags`: 
+- `PuzzleId`: `string`, the puzzle's unique identifier.
+- `FEN`: `string`, the FEN string of the position before the opponent makes their move.
+- `Moves`: `string`, the solution to the puzzle. All player moves of the solution are "only moves", i.e. playing any other move would considerably worsen the player position. An exception is made for mates in one: there can be several. Any move that checkmates should win the puzzle.
+- `Rating`: `int`, the Glicko-2 rating of the puzzle.
+- `RatingDeviation`: `int`, the Glicko-2 rating deviation of the puzzle.
+- `Popularity`: `int`, a number between `100` (best) and `-100` (worst), calculated as `100 * (upvotes - downvotes)/(upvotes + downvotes)`. Votes are weighted by various factors such as whether the puzzle was solved successfully or the solver's puzzle rating in comparison to the puzzle's.
+- `NbPlays`: `int`, the number of times a puzzle was played.
+- `Themes`: `string`, a space separated list of puzzle themes.
+- `GameUrl`: `string`, the link to the puzzle on https://lichess.org
+- `OpeningTags`: `string`, a space separated list of openings. This is only set for puzzles starting before move 20.
+
+For a list of all possible puzzle themes and their description: https://github.com/ornicar/lila/blob/master/translation/source/puzzleTheme.xml
+For a list of all possible openings: https://github.com/lichess-org/chess-openings
+
+#TODO: link to https://lichess.org/@/lichess/blog/new-puzzles-are-here/X-S6gRUA and https://lichess.org/study/viiWlKjv