picobsd: add deprecation notices

Notices appear both in picobsd(8) (near the top for easy notice) and are
also printed to stderr on every invocation of picobsd for visibility.

The tentative date for removal is October 31st, as no volunteers have
stepped forward at all from postings to -arch@ at least.

No objection from:	-arch@
MFC after:	3 days

release/picobsd/build/picobsd

@@ -1019,6 +1019,7 @@ set_build_parameters() {
 # Main entry of the script. Initialize variables, parse command line
 # arguments.
 
+1>&2 echo "WARNING: picobsd is deprecated and will be removed in FreeBSD 13.0."
 
 set_defaults
 while [ true ]; do

share/man/man8/picobsd.8

@@ -1,6 +1,6 @@
 .\" -*- nroff-fill -*-
 .\" $FreeBSD$
-.Dd October 1, 2013
+.Dd October 20, 2019
 .Dt PICOBSD 8
 .Os
 .Sh NAME
@@ -11,6 +11,10 @@
 .Op Ar options
 .Op Ar config-name Op Ar site-name
 .Sh DESCRIPTION
+.Nm
+is deprecated and will be removed in
+.Fx 13.0 .
+.Pp
 The
 .Nm
 utility is a script which produces a minimal implementation of