Explain running MCP server without a config file

Author: jcaudle

docs/source/command-reference.mdx

@@ -88,6 +88,7 @@ iwr 'https://mcp.apollo.dev/download/win/v0.6.1' | iex
 ## Usage
 
 Configure the Apollo MCP server with a YAML configuration file. The path to this file is the only argument.
+A configuration file is not required, but if one is not provided environment variables for your Apollo Graph Reference and Apollo Key are needed.
 
 ```sh showLineNumbers=false
 apollo-mcp-server [OPTIONS] <PATH/TO/CONFIG/FILE>