Let an editor add users.

editor.php

<?php   

/**
  * Let editor manage users
  */ 
function make_allow_editor_to_add_users() {
	$edit_editor = get_role( 'editor' );
	$edit_editor->add_cap( 'list_users' ); 
	$edit_editor->add_cap( 'create_users' );
	$edit_editor->add_cap( 'delete_users' );
}

add_action( 'admin_init', 'make_allow_editor_to_add_users' );