doc: align code example with actual code behavior

module.createRequireFromPath() takes a filename as argument.
But the accompanying code example in the documentation makes it seem
like it can take a directory argument as well.
However, if a directory is passed as argument instead of a filename,
then the function does not work as expected.

Therefore, the fix is to make explicit in the code example that
only filenames could be passed to module.createRequireFromPath()
and not directory names.

Fixes: #23710
Refs: #24763 (comment)

doc/api/modules.md

@@ -919,7 +919,7 @@ added: v10.12.0
 
 ```js
 const { createRequireFromPath } = require('module');
-const requireUtil = createRequireFromPath('../src/utils');
+const requireUtil = createRequireFromPath('../src/utils/index.js');
 
 // Require `../src/utils/some-tool`
 requireUtil('./some-tool');