How to add new payment gateway

Hi
I need to add one of the payment gateways from Omnigithub.
I installed it with

composer require league/omnipay GWNAME

in

 /var/www/html/invoices/vendor/omnipay/GWNAME

But the gateway is not shown in available payment gateways.
Anyone know how should I add new one?

Make feature request propose fork/pull request on Github, for 1.6.beta2 or 2, submit info on Ominipay to version 1 or 2 slack channel