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

bin/sh/sh.1

@@ -1,4 +1,6 @@
 .\"-
+.\" SPDX-License-Identifier: BSD-3-Clause
+.\"
 .\" Copyright (c) 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
 .\"
@@ -1074,7 +1076,6 @@ or the end of the
 command.
 .Ss Grouping Commands Together
 Commands may be grouped by writing either
-.Pp
 .Sm off
 .Bd -literal -offset indent
 .Po Ar list Pc
@@ -2923,7 +2924,9 @@ This version of
 was rewritten in 1989 under the
 .Bx
 license after the Bourne shell from
-.At V.4 .
+.At V.4
+and first appeared in
+.Bx 4.3 Net/2 .
 .Sh AUTHORS
 This version of
 .Nm