Feat: Write comprehensive crate README

Co-authored-by: Opus 4.6 <noreply@anthropic.com>

README.md

@@ -1,2 +1,69 @@
-# ZWUS-rs
-Zero Width Unicode Standard - Crate
+# Zero Width Unicode Standard (ZWUS)
+
+Zero Width Unicode Steganography — hide text inside invisible characters.
+
+```toml
+[dependencies]
+zwus = "0.1"
+```
+
+## Usage
+
+```rust
+use zwus::Zwus;
+
+// Encode & decode strings
+let hidden = Zwus::encode_string("secret");
+let revealed = Zwus::decode_to_string(&hidden);
+assert_eq!(revealed, "secret");
+
+// Encode & decode number arrays
+let encoded = Zwus::encode_number_array(&[72, 101, 108]);
+let decoded = Zwus::decode_to_number_array(&encoded);
+assert_eq!(decoded, vec![72, 101, 108]);
+```
+
+### Base
+
+Higher base = shorter output, but more likely visible in some renderers.
+
+```rust
+Zwus::encode_string_with_base("hi", 3); // default, safest
+Zwus::encode_string_with_base("hi", 6); // compact
+Zwus::encode_string_with_base("hi", 8); // most compact
+```
+
+Decode must match the encode base:
+
+```rust
+Zwus::decode_to_string_with_base(&encoded, 6);
+```
+
+### Embedded in visible text
+
+Non-ZWUS characters are automatically ignored during decoding, so hidden payloads survive being mixed into normal text.
+
+```rust
+let hidden = Zwus::encode_string("secret");
+let carrier = format!("nothing to see here{hidden}, move along");
+let extracted = Zwus::decode_to_string(&carrier);
+assert_eq!(extracted, "secret");
+```
+
+### Full Unicode support
+
+Handles emoji and all of Unicode — anything `char` can represent.
+
+```rust
+let encoded = Zwus::encode_string("hello 🦀🔥");
+let decoded = Zwus::decode_to_string(&encoded);
+assert_eq!(decoded, "hello 🦀🔥");
+```
+
+## Interop
+
+Encoded output is byte-identical to the [npm package](https://www.npmjs.com/package/zwus), so you can encode in JS and decode in Rust or vice versa.
+
+## License
+
+[WTFPL](LICENSE)