doc: mark --import as experimental

PR-URL: #44067
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

Author: MoLow

doc/api/cli.md

@@ -601,6 +601,8 @@ Specify ICU data load path. (Overrides `NODE_ICU_DATA`.)
 added: REPLACEME
 -->
 
+> Stability: 1 - Experimental
+
 Preload the specified module at startup.
 
 Follows [ECMAScript module][] resolution rules.