improve esm docs

- clarify extension resolving

Author: vankop

src/content/guides/ecma-script-modules.mdx

@@ -79,7 +79,7 @@ In DataURIs using the `text/javascript` or `application/javascript` mime type wi
 
 In addition to the module format, flagging modules as ESM also affect the resolving logic, interop logic and the available symbols in modules.
 
-Imports in ESM are resolved more strictly. Relative requests must include a filename and file extension.
+Imports in ESM are resolved more strictly and require file extension (e.g. `*.js` or `*.mjs`) if you specify relative request. Relative requests must include a filename and file extension.
 
 T> Requests to packages e.g. `import "lodash"` are still supported.