add a new article to describe adding customer menu item

[khairuzzaman]

Dear Admin, When I try to add a new menu in the customer section I face some problems. After doing some R&D I was able to add the menu. I think it will be good if there is an article in the official documentation. So I add a new article to the documentation. If it is worth having you can merge the pull request. :)

Regards Abu Zafor Khairuzzaman

[DmitriyKulagin]

@khairuzzaman We appreciate your work, but we do not add articles to the documentation other than those required or stated in the "Issues" tab. This is due to the fact that we try to concentrate in the documentation only the most important or frequently used guides by developers. However, if you want to share your experience, then I recommend creating a topic on our forum - in this context, your example will be very useful to the community. Thank you!