The third parameter of the add_menu_page() function is $capabilities
, which represents:
"The capability required for this menu to be displayed to the user."
In your case you set 'add_users'
, which is a capability that only the admin users have, so it will be only displayed to administrators.
You just need to change it to other capability that editors have, for example 'edit_pages'
.
Note that this will make it visible for editors and also for admins, since they also have that capability.
See the complete list of WordPress Roles & Capabilities for further info.