sh.1: update history + spdx + linter error

+ increase history consistency by adding "first appeared"
+ remove a skipped new paragraph macro to quiet linter
+ tag spdx

MFC after: 3 days
History source: www.in-ulm.de/~mascheck/various/ash/#bsd

Reviewed by: mhorne,imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1440