Make it easier to install this on FreeBSD: Create a port

There are multiple options how to do that:

* I could first create a port for debops the command (if it doesn't exist yet), and then a second port that installs anotherkamila/debops to somewhere where debops will find it and use it instead of the official repo. For that, I'd need debops to look for the repo in a system-wide location though, which it currently doesn't AFAIK.

* I could create a bsdops port, which would be just the debops the command port, but patched to download my fork instead of the official one. This would also make it possible to rename the command to `bsdops` and keep a separate `debops` command that defaults to the official repo. That separation might be a good idea. +1 for this solution.