[doc] develop payment gateway on top of payum
[doc] develop payment gateway on top of payum

Payum/Payum,formapro-forks/Payum,fullpipe/Payum,staabm/Payum,fullpipe/Payum,StoreFactory/Payum,StoreFactory/Payum,digisec/Payum,digisec/Payum,Payum/Payum,aitboudad/Payum,formapro-forks/Payum,StoreFactory/Payum,ASKozienko/Payum