Add hocon.conf

[ustc-zzzz]

According to official specification:

Empty files are invalid documents

A valid file of HOCON format can be empty.

[mathiasbynens]

Care to submit a PR?

[ustc-zzzz]

Well, my initial thought was that the changes are so small that sending a PR is seemed to use a sledgehammer to crack a nut, but since it is asked, I might as well create a PR.