docs: update the usage (#17)

README.md

@@ -6,14 +6,76 @@
 [![docs.rs](https://docs.rs/csa/badge.svg)](https://docs.rs/csa)
 
 A Shogi game serialization/deserialization library in CSA format.
+CSA format is a plaintext format for recording Shogi games. This library supports parsing CSA-formatted string as well as composing CSA-formatted string from structs. Detail about CSA format is found at [here](http://www.computer-shogi.org/protocol/record_v22.html).
 
-[Documentation](https://nozaq.github.io/csa-rs)
+[Documentation](https://docs.rs/csa)
 
 ## Usage
 
-```toml
-[dependencies]
-csa = "1.0"
+Below is an example of parsing CSA-formatted string into structs.
+
+```rust
+use std::time::Duration;
+use csa::{parse_csa, Action, Color, GameRecord, MoveRecord, PieceType, Square};
+
+let csa_str = "\
+V2.2
+N+NAKAHARA
+N-YONENAGA
+$EVENT:13th World Computer Shogi Championship
+PI
++
++2726FU
+T12
+";
+
+let game = parse_csa(csa_str).expect("failed to parse the csa content");
+assert_eq!(game.black_player, Some("NAKAHARA".to_string()));
+assert_eq!(game.white_player, Some("YONENAGA".to_string()));
+assert_eq!(game.event, Some("13th World Computer Shogi Championship".to_string()));
+assert_eq!(game.moves[0],  MoveRecord{
+    action: Action::Move(Color::Black, Square::new(2, 7), Square::new(2, 6), PieceType::Pawn),
+    time: Some(Duration::from_secs(12))
+});
+```
+
+In contrast, structs can be composed into CSA-formatted string.
+
+```rust
+use std::time::Duration;
+use csa::{ Action, Color, GameRecord, MoveRecord, PieceType, Square};
+
+let mut g = GameRecord::default();
+g.black_player = Some("NAKAHARA".to_string());
+g.white_player = Some("YONENAGA".to_string());
+g.event = Some("13th World Computer Shogi Championship".to_string());
+g.moves.push(MoveRecord {
+    action: Action::Move(
+        Color::Black,
+        Square::new(2, 7),
+        Square::new(2, 6),
+        PieceType::Pawn,
+    ),
+    time: Some(Duration::from_secs(5)),
+});
+g.moves.push(MoveRecord {
+    action: Action::Toryo,
+    time: None,
+});
+
+let csa_str = "\
+V2.2
+N+NAKAHARA
+N-YONENAGA
+$EVENT:13th World Computer Shogi Championship
+PI
++
++2726FU
+T5
+%TORYO
+";
+
+assert_eq!(csa_str, g.to_string());
 ```
 
 ## License