feat: add .env.example file

.env.example

@@ -0,0 +1,9 @@
+# VOICEVOXの設定
+VOICEVOX_HOST=http://localhost:50021
+VOICEVOX_SPEAKER_ID=3
+VOICEVOX_STYLE_ID=2
+
+# OpenAIの設定
+OPENAI_API_KEY=your-openai-api-key
+OPENAI_API_ENDPOINT=https://api.openai.com/v1
+OPENAI_MODEL_NAME=gpt-4o-mini