Added more examples to the .env.example file.

.env.example

@@ -1,9 +1,38 @@
+# .env.example
+
+# OpenAI API key for accessing OpenAI's GPT models
 OPENAI_API_KEY=
+
+# API key for accessing Tavily's services
 TAVILY_API_KEY=
+
+# API key for accessing LangChain's services
 LANGCHAIN_API_KEY=
+
+# Path to the directory where documents are stored
 DOC_PATH=./my-docs
 
-# the name of the embedding model to use for Ollama
+# The name of the embedding model to use for Ollama
 OLLAMA_EMBEDDING_MODEL=
-# the Ollama endpoint to use
-OLLAMA_BASE_URL=
+
+# The Ollama endpoint to use
+OLLAMA_BASE_URL=
+
+# Choose one of the available retrievers by uncommenting the desired retriever:
+# RETRIEVER=arxiv
+# RETRIEVER=bing
+# RETRIEVER=custom
+# RETRIEVER=duckduckgo
+# RETRIEVER=exa
+# RETRIEVER=google
+# RETRIEVER=searx
+# RETRIEVER=semantic_scholar
+# RETRIEVER=serpapi
+# RETRIEVER=serper
+# RETRIEVER=tavily
+
+# Example setting for retriever
+RETRIEVER=tavily
+
+# Maximum number of search results to return per query
+MAX_SEARCH_RESULTS_PER_QUERY=5