docs(readme): add instructions for FreeBSD

[DtxdF]

Description

Add instructions for FreeBSD and related things to use rustypaste on that platform.

Motivation and Context

I created a port a while ago, and recently created a Makejail (a Dockerfile-like file, but for AppJail) for rustypaste, so I think users can benefit from those things to use rustypaste on FreeBSD.

How Has This Been Tested?

I have installed rustypaste using the official FreeBSD package and I have also tested rustypaste using Makejail on my notebook and on my production server where I currently host rustypaste.

I have tried a lot of combinations when using Makejail, much better described in the repository where Makejail is hosted.

For each rustypaste update I test the new and old features by simply modifying rustypaste.toml and test it with rpaste as client.

Changelog Entry

Added

• Instructions for install rustypaste on FreeBSD.
• AppJail to Features section.

Types of Changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Documentation (no code change)
• [ ] Refactor (refactoring production code)
• [ ] Other

Checklist:

• [x] My code follows the code style of this project.
• [x] I have updated the documentation accordingly.
• [ ] I have formatted the code with rustfmt.
• [ ] I checked the lints with clippy.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

:loudspeaker: Thoughts on this report? Let us know!.