Добавить двуязычную документацию (русский и английский) (#1101)

docs/EN/TestDc.md

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+# Telegram Test Environment (Test DCs)
+
+Traffic routing to Telegram test data centers (test environment).
+Useful for developing/testing bots and clients within the Telegram test environment.
+
+## How to Enable
+
+**Automatically.** Telegram Desktop marks test DCs with a +10000
+offset (10001–10003). The proxy automatically detects this offset — no configuration needed, allowing
+you to use production and test accounts simultaneously in a single client.
+
+**Forced.** For clients that report test DCs as standard 1-3
+(Telethon, TDLib) — they cannot be detected automatically. In this case, all traffic
+is forcibly routed to test DCs (production accounts will stop working through this proxy).
+To force this behavior, use the `--force-test-dc` flag in CLI:
+
+```bash
+tg-ws-proxy --force-test-dc      # + your --secret / --port
+```
+
+## Limitations
+
+Only works for **direct DC → IP** and **Cloudflare Worker** routes (see [Setting up a Cloudflare Worker](./CfWorker.md)).