doc: add command flag to import.meta.resolve

import.meta.resolve is only available under
--experimental-import-meta-resolve cli flag.

Source:
https://github.com/nodejs/node/blob/e46c680bf2b211bbd52cf959ca17ee98c7f657f5/lib/internal/modules/esm/translators.js#L132

PR-URL: #38171
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/esm.md

@@ -283,6 +283,9 @@ const buffer = readFileSync(new URL('./data.proto', import.meta.url));
 
 > Stability: 1 - Experimental
 
+This feature is only available with the `--experimental-import-meta-resolve`
+command flag enabled.
+
 * `specifier` {string} The module specifier to resolve relative to `parent`.
 * `parent` {string|URL} The absolute parent module URL to resolve from. If none
   is specified, the value of `import.meta.url` is used as the default.