Better describe columns

README.md

@@ -2,12 +2,14 @@
 license: cc0-1.0
 ---
 
-# fishnet-evals
+# Lichess database positions with Stockfish evaluations
 
-Chess positions and evaluations computed using Lichess's distributed Stockfish analysis.
+Positions with evaluations extracted from https://database.lichess.org/.
 
-## Columns
+Evaluations were computed using Lichess's distributed Stockfish analysis [fishnet](https://github.com/lichess-org/fishnet), using various Stockfish versions.
 
-* `fen`: FEN of the position. En passant square only included if fully legal en passant available.
-* `cp` / `mate`: Evaluation of the position in centipawns or moves to mate. Exactly one of these is not null. Positive if White has the advantage.
-* `move`: UCI of the next move played by the human player, if any. Uses Chess960 (king to rook) notation for castling.
+column | type | description
+--- | --- | ---
+`fen` | string | FEN of the evaluated position. En passant square included only if a fully legal en passant move exists.
+`cp` / `mate` | int *or* null | Signed evaluation of the position in centipawns or moves to mate, as computed by Stockfish. Exactly one of these is not null. Always given from White's point of view, so positive if White has the advantage
+`move` | string *or* null | UCI notation of the next move played by the human player, if any. Always in Chess960 mode (king move to rook for castling).