Add instructions to the README

Author: triarius

README.md

@@ -3,3 +3,33 @@
 Parses GitHub CODEOWNERS[^1] files.
 
 [^1]: See https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners
+
+## Installation
+```sh
+cargo install --git https://github/triarius/git-codeowners.git
+```
+
+To invoke this as `git codeowners` instead of `/path/to/git-codeowners`, ensure that
+1. `git` is installed and in your `PATH`
+2. The location `cargo` installs executables to is in your `PATH`. This is typically `~/.local/share/cargo/bin`.
+
+## Usage
+Change directory to a git repo with a CODEOWNERS file.
+
+```
+Usage: git-codeowners [OPTIONS] <COMMAND>
+
+Commands:
+  find  Find owners for the specified paths. Reads paths from STDIN if not provided as positional arguments
+  help  Print this message or the help of the given subcommand(s)
+
+Options:
+  -p, --path <PATH>  Path to the CODEOWNERS file [default: .github/CODEOWNERS]
+  -h, --help         Print help
+  -V, --version      Print version
+```
+
+### Detecting CODEOWNERS of all files changed in a branch
+```sh
+git diff (git merge-base origin/main HEAD) --name-only | git codeowners find
+```