[docgen] Update doc/neogen.txt

skip-checks: true

doc/neogen.txt

@@ -133,6 +133,8 @@ Neogen provides those defaults, and you can change them to suit your needs
    }
 <
   Default configurations for a languages can be found in `lua/neogen/configurations/<your_language>.lua`
+  To use an existing configuration in another file type, you can do like: `cuda = require("neogen.configurations.cpp")` 
+  for your language.
 
  - To know which snippet engines are supported, take a look at |neogen-snippet-integration|.
    Example: `snippet_engine = "luasnip"`