docs: add pipeline architecture flow diagram

README.md

@@ -9,6 +9,29 @@ Scythe is a native, ultra-lightweight alternative to NVIDIA ShadowPlay and GPU S
 
 ---
 
+## Pipeline Architecture
+
+```text
+[ Desktop Surface ]
+  │
+  ├── Wayland : ashpd screencast ──> PipeWire DMA-BUF fd (zero-copy)
+  ├── X11     : XCB MIT-SHM      ──> Shared Memory frame pool
+  └── Windows : D3D11 DXGI       ──> Desktop Duplication texture
+  │
+  ▼
+[ Hardware Encoder Surface ]
+  ├── NVENC / AMF / QSV / VAAPI  (direct hardware ingest)
+  └── libx264 / libx265 / libsvtav1 (CPU fallback)
+  │
+  ▼
+[ Memory Ring Buffer ] ──(Ctrl+Shift+R)──> [ MP4 Muxer (AVPacket Rebase) ] ──> ~/Videos/Scythe/
+  │ (rolling circular buffer)
+  ▼
+[ Live Stream / Record Engine ] ─────────> Local MP4 / RTMP Broadcast
+```
+
+---
+
 ## Features
 
 - **Instant Replay Buffer**: Constantly records gameplay into a high-speed in-memory circular ring buffer. Save the last 15s to 5 minutes of action instantly with one hotkey (`Ctrl+Shift+R`) without writing temporary files to disk.