Update FreeNAS/TrueNAS CORE installation guide

[DogmaDragon]

In v0.24 release, FreeBSD binary was added. Current documentation is outdated.

Link: https://docs.stashapp.cc/installation/freenas-truenas/

[reedy]

5b56e04 mentions it...

[animalrap]

would be awesome to update the docs for truenas as well, especially since truecharts is not around anymore.