update README
update README

deepikaarora04/salesforce-custom-activity,gianluigimorsellib-i/HelloWorldApp,kratigarg1/newRepoPOC,ExactTarget/journey-builder-custom-hello-world,rbudakoti/hello_world,eddiecliff/HelloWorld,gianluigimorsellib-i/HelloWorldApp,payman81/je-voucher,deepikaarora04/salesforce-custom-activity,aalmanza0705/journey-builder-custom-hello-world,payman81/je-voucher,rbudakoti/hello_world,kratigarg1/newRepoPOC,BillyLoizou/journey-builder-custom-hello-world,aalmanza0705/journey-builder-custom-hello-world