Merge pull request #145 from netbootxyz/claude/pr-144-20250714_042331

docs: fix custom menu chain command from custom/custom.ipxe to custom.ipxe

Author: antonym

docs/docker/custom-menus.md

@@ -45,7 +45,7 @@ chain custom/custom.ipxe
 
 With:
 ```bash
-chain custom/custom.ipxe
+chain custom.ipxe
 ```
 
 ### Step 4: Configure Your Custom Menu