Add .env.example file for environment variable configuration

- Introduced a new `.env.example` file to provide a template for required environment variables, including API keys and project settings.
- This addition aids in setting up the development environment and ensures consistency in configuration across team members.

.env.example

@@ -0,0 +1,11 @@
+OPENAI_API_KEY=
+PINECONE_API_KEY=
+LANGSMITH_TRACING=true
+
+PINECONE_INDEX_NAME=chassidus-index
+PINECONE_ENVIRONMENT=starter
+LANGSMITH_ORG_ID=
+LANGSMITH_API_KEY=
+
+LANGSMITH_ENDPOINT="https://api.smith.langchain.com"
+LANGSMITH_PROJECT="pr-essential-pomelo-22"