docs: actually write README

README.md

@@ -1 +1,49 @@
 # jj-cz: Conventional Commits for Jujutsu
+
+An interactive CLI tool that guides Jujutsu users through creating
+[conventional commit](https://www.conventionalcommits.org/) messages.
+
+## Features
+
+- Interactive prompts for type, scope, and description
+- All 11 commit types with descriptions (feat, fix, docs, style,
+  refactor, perf, test, build, ci, chore, revert)
+- Optional scope with validation
+- 72-character first-line limit enforcement
+- Preview before applying
+- Clean cancellation with Ctrl+C
+
+## Usage
+
+No fancy tricks, just run `jj-cz`.
+
+```sh
+jj-cz
+```
+
+The tool detects whether you're in a Jujutsu repository, guides you
+through the commit message, and applies it to your current change.
+
+## Requirements
+
+- A Jujutsu repository
+- An interactive terminal
+
+You don’t need `jj` itself to be installed at all, though I’m not sure
+what `jj-cz` alone would be good for without `jj`.
+
+## Exit Codes
+
+| Code | Meaning                                              |
+|------|------------------------------------------------------|
+| 0    | Success or clean cancellation                        |
+| 1    | Error (invalid input, repository issues, jj failure) |
+| 130  | Interrupted                                          |
+
+## Installation
+
+You can install jj-cz with Cargo by building it from source.
+
+```sh
+cargo install --path .
+```