docs(readme): add Full Tunnel mode section

The main README had no mention of Full Tunnel mode beyond passing
references in the FAQ. Add a dedicated section between "How it works"
and "Quick Start" that explains what Full Tunnel is, why you'd use it
(YouTube, UDP, quota), the architecture diagram, and what you need to
set it up.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yyoyoian-pixel

README.md

@@ -45,6 +45,49 @@
 
 ISPs can't read inside encrypted HTTPS. They only see the address — `www.google.com`. The actual page lookup happens inside Google's network, hidden in the encrypted tunnel.
 
+### Full Tunnel mode
+
+The default **apps_script** mode relays each HTTP request through Google. This works great for browsing, but has limits: YouTube video chunks are blocked by Google internally, UDP protocols (Telegram voice, gaming) can't pass through, and every request counts against your daily Apps Script quota.
+
+**Full Tunnel mode** removes those limits by adding a small relay server (tunnel-node) on a VPS you control:
+
+```
+   you  →  browser  →  mhrv-rs  ──┐
+                                  │ ISP only sees:  www.google.com
+                                  ▼
+                          Google's network
+                                  │
+                                  ▼
+                     Apps Script forwards to your VPS
+                                  │
+                                  ▼
+                        tunnel-node (your VPS)
+                                  │
+                                  ▼
+                    real TCP connection to any site
+```
+
+Every TCP connection from your device is tunneled end-to-end: mhrv-rs multiplexes all your traffic into batched requests through Apps Script, your tunnel-node opens real TCP sockets to the destination. YouTube, Telegram, WebSockets, anything TCP — it all works.
+
+**What you need:**
+- Everything from the Quick Start (Apps Script + auth key)
+- A VPS with a public IP (any cheap $5/mo provider works)
+- Deploy [`CodeFull.gs`](assets/apps_script/CodeFull.gs) instead of `Code.gs`
+- Deploy the [tunnel-node](tunnel-node/) on your VPS (Docker one-liner)
+
+**In your config:**
+```json
+{
+  "mode": "full",
+  "script_ids": ["your-deployment-id"],
+  "auth_key": "your-secret"
+}
+```
+
+No certificate installation needed — Full Tunnel doesn't MITM your TLS. The tunnel-node handles real connections server-side.
+
+For step-by-step setup, see the [tunnel-node README](tunnel-node/README.md).
+
 ## Quick Start
 
 **About 5 minutes.** You need: