Add FreeBSD support

[drupaladmin]

Releem Agent cound be installed on Linux and as a Docker container

The issue on how to run Releem Agent manually on FreeBSD #203

Please add FreeBSD support

[drupaladmin]

How to run Releem Agent on the FreeBSD manually - #203

[manswiss]

See #203 (comment) with a nearly working version. It gives an idea how it can be done. I think the effort is not very big to bring it work.