docs(cargo): add readme and documentation fields for crates.io

Author: dodoflix

Cargo.toml

@@ -7,6 +7,8 @@ license      = "MIT"
 repository   = "https://github.com/oxidized-mc/codec"
 homepage     = "https://github.com/oxidized-mc/codec"
 rust-version = "1.85"
+readme       = "README.md"
+documentation = "https://docs.rs/oxidized-codec"
 description  = "Minecraft protocol codec — VarInt/VarLong encoding, Packet trait, wire-format type readers/writers, frame encoding"
 keywords     = ["minecraft", "oxidized-mc"]
 categories   = ["game-development"]