docs: update installation instructions and version in README

README.md

@@ -14,6 +14,48 @@ Generate **Conventional Commits** messages, pull request descriptions, code revi
 
 ---
 
+## Installation
+
+`gai` runs on the [Bun](https://bun.sh) runtime. Install Bun first if you don't have it:
+
+```bash
+curl -fsSL https://bun.sh/install | bash
+```
+
+Then install `gai` globally from npm:
+
+```bash
+# npm
+npm install -g @mplan/gai
+
+# Bun
+bun add -g @mplan/gai
+```
+
+Or run it once without installing:
+
+```bash
+bunx @mplan/gai
+# or
+npx @mplan/gai
+```
+
+After installing, the `gai` command is available everywhere. Run `gai config` to set your API key, then `gai` to open the interactive menu.
+
+<details>
+<summary><strong>From source (development)</strong></summary>
+
+```bash
+git clone https://git.catpl.top/Mplan/gai.git
+cd gai
+bun install
+bun link   # makes `gai` point to your local checkout
+```
+
+</details>
+
+---
+
 ## Features
 
 - **🤖 AI Commit Messages** — generate Conventional Commits from staged diffs with project context
@@ -121,7 +163,7 @@ git diff | gai suggest branch
 Run `gai` without arguments to open the mole-style interactive menu:
 
 ```
-  gai v0.1.3
+  gai v0.1.4
   AI-powered git helper for commits, PRs, reviews, and changelogs
   ────────────────────────────────────────────────────────────────────────