docs: expand README with overview, features, and how-it-works

Add project overview, feature breakdown (Capture/Compose/Export), the
Install→Grant→Record→Export flow, auto-update notes, tech stack, download +
product-page links, requirements, and license — sourced from the portfolio
landing page. Correct the release note to the tag-triggered release.yml pipeline.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: jasonzh0

README.md

@@ -1,6 +1,53 @@
 # CineScreen
 
-Native macOS screen recording app — Swift / SwiftUI / Metal.
+> Cinematic screen recording for macOS — turn raw captures into polished product videos.
+
+Native macOS screen recorder built in Swift, SwiftUI, and Metal. Capture any
+window, display, or region with **ScreenCaptureKit**; polish it in a per-frame
+timeline editor with smooth cursor motion, automatic zooms, and gradient
+backdrops; then export through an **AVAssetWriter** pipeline that never drops a
+frame.
+
+Free and open source (MIT) · macOS 14+ · Apple Silicon & Intel.
+
+**[⬇ Download for Mac](https://github.com/jasonzh0/CineScreen/releases/latest)** · [Product page & demo](https://jasonzhang.dev/apps/cinescreen)
+
+## Features
+
+### 🎥 Capture — pixel-perfect ScreenCaptureKit
+Apple's native capture API drives every frame. Pick a window, a display, or a
+region — CineScreen pipes the raw stream straight into a Metal compositor.
+
+### ✨ Compose — polish without thinking
+Smooth cursor motion, automatic click highlights, and zoom keyframes you tune
+in the timeline. Style recordings with gradient backdrops, padding, and rounded
+window chrome.
+
+### 📦 Export — AVAssetWriter, no compromises
+A dedicated export compositor renders the final video offline at a locked frame
+rate. ProRes or H.264, no dropped frames, signed and notarized `.dmg`.
+
+## How it works
+
+A whole studio in your menu bar. CineScreen sits quietly until you need it — tap
+record, pick a window, and the editor opens with your clip already loaded.
+
+1. **Install** — drag CineScreen into Applications; the menu-bar icon appears on first launch.
+2. **Grant access** — enable Screen Recording for CineScreen in System Settings, then relaunch.
+3. **Record** — open the floating control bar, pick a window or display, hit record. Stop, and your clip drops straight into the editor.
+4. **Export** — style, scrub, and tune; the Metal compositor renders every frame offline at a locked frame rate.
+
+## Auto-updates
+
+CineScreen updates itself in place via [Sparkle](https://sparkle-project.org).
+Because the app is replaced at its existing path, macOS keeps the Screen
+Recording / Accessibility permissions you already granted — **no re-granting
+after updates**. The app verifies each download against an embedded EdDSA key
+before installing. See [docs/UPDATES.md](docs/UPDATES.md) for the full pipeline.
+
+## Tech stack
+
+`Swift 5.9` · `SwiftUI` · `Metal` · `ScreenCaptureKit` · `AVFoundation` · `AVAssetWriter` · `AppKit` · [`Sparkle`](https://github.com/sparkle-project/Sparkle)
 
 ## Bootstrap
 
@@ -36,7 +83,10 @@ xcrun notarytool store-credentials cinescreen-notary \
   --password APP-SPECIFIC-PASSWORD
 ```
 
-CI handles signing + notarization in `.github/workflows/build.yml`.
+**Cutting a release:** bump `MARKETING_VERSION` in `project.yml`, commit, then push a
+`vX.Y.Z` tag. The `.github/workflows/release.yml` pipeline signs with Developer ID,
+notarizes, publishes the GitHub Release, and deploys the Sparkle appcast to GitHub
+Pages — which auto-updates existing users.
 
 ## Layout
 
@@ -45,9 +95,10 @@ CI handles signing + notarization in `.github/workflows/build.yml`.
 ├── project.yml              # XcodeGen spec
 ├── Makefile                 # build/sign/notarize targets
 ├── exportOptions.plist      # xcodebuild -exportArchive options
-├── scripts/
+├── scripts/                 # make_release.sh (archive→sign→notarize→DMG/appcast)
+├── docs/                    # UPDATES.md (Sparkle auto-update setup)
 └── CineScreen/
-    ├── App/                 # @main + root views
+    ├── App/                 # @main + root views, Sparkle updater
     ├── Capture/             # ScreenCaptureKit + mouse tracking
     ├── Compositor/          # Metal renderer
     ├── ControlBar/          # floating control bar window
@@ -61,6 +112,12 @@ CI handles signing + notarization in `.github/workflows/build.yml`.
     └── Resources/           # Assets.xcassets, Info.plist, entitlements
 ```
 
-## Min macOS
+## Requirements
+
+macOS 14 (Sonoma) or later · Apple Silicon & Intel.
+
+## License
 
-14.0 (Sonoma).
+MIT — see [LICENSE](LICENSE).
+</content>
+</invoke>