Update composition.mdx

docs/servers/composition.mdx

@@ -205,11 +205,17 @@ This was the default format in FastMCP before 2.4. While still supported, it's n
 
 ### Configuring the Prefix Format
 
-You can configure the prefix format globally:
+You can configure the prefix format globally in code:
 
 ```python
 from fastmcp import settings
-settings.settings.resource_prefix_format = "protocol"  # Switch to legacy format
+settings.settings.resource_prefix_format = "protocol" 
+```
+
+Or via environment variable:
+
+```bash
+FASTMCP_RESOURCE_PREFIX_FORMAT=protocol
 ```
 
 Or per-server: