documentation: Fix minor typos

• explaining-bsd: fix missing opening quote in trademarks list
• committers-guide: remove duplicate word ("to to" -> "to")
• jails: fix article usage ("A incomplete" -> "An incomplete")
• zfs: remove redundant preposition ("in since" -> "since")

Reviewed by: ziaee
Closes: https://github.com/freebsd/freebsd-doc/pull/624