[centos-7-erlang] fix and improve centos 7 epel note for erlang
[centos-7-erlang] fix and improve centos 7 epel note for erlang

palourde/sensu-docs,solarkennedy/sensu-docs,solarkennedy/sensu-docs,palourde/sensu-docs,solarkennedy/sensu-docs,solarkennedy/sensu-docs