identifying_to_services.rst: fix cert add

NickServ is usually server-side alias on all networks that also checks that we are sending message to Services and if we aren't, the sending is aborted. Try it with `/quote NickServ help` or even `/allserv quote NickServ help`.
Merge pull request #42 from Mkaysi/patch-2

identifying_to_services.rst: fix cert add