docs: add .env.example for 0G provider credentials

.env.example

@@ -0,0 +1,21 @@
+# Copy to .env and fill in. Generate keys with:
+#   0g-compute-cli inference get-secret --provider <PROVIDER_ADDRESS> --duration 0
+# Each 0G provider has its OWN host + key (a key is bound to one provider).
+
+# --- Chat / reasoning (e.g. zai-org/GLM-5-FP8) ---
+OG_CHAT_BASE_URL=https://<chat-host>.integratenetwork.work/v1/proxy
+OG_CHAT_MODEL=zai-org/GLM-5-FP8
+OG_CHAT_PROVIDER=0x...
+OG_CHAT_API_KEY=app-sk-...
+
+# --- Speech-to-text (e.g. openai/whisper-large-v3) ---
+OG_STT_BASE_URL=https://<stt-host>.integratenetwork.work/v1/proxy
+OG_STT_MODEL=openai/whisper-large-v3
+OG_STT_PROVIDER=0x...
+OG_STT_API_KEY=app-sk-...
+
+# --- Vision (optional; e.g. qwen/qwen3-vl-30b-a3b-instruct). Leave blank to disable. ---
+OG_VISION_BASE_URL=
+OG_VISION_MODEL=qwen/qwen3-vl-30b-a3b-instruct
+OG_VISION_PROVIDER=0x...
+OG_VISION_API_KEY=