Document the removed 'dist' target

Also adds missing copyright boilerplate to util/mktar.sh

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/7696)

CHANGES

@@ -9,6 +9,11 @@
 
  Changes between 1.1.1 and 1.1.2 [xx XXX xxxx]
 
+  *) Remove the 'dist' target and add a tarball building script.  The
+     'dist' target has fallen out of use, and it shouldn't be
+     necessary to configure just to create a source distribution.
+     [Richard Levitte]
+
   *) Recreate the OS390-Unix config target.  It no longer relies on a
      special script like it did for OpenSSL pre-1.1.0.
      [Richard Levitte]

util/mktar.sh

@@ -1,4 +1,10 @@
 #! /bin/sh
+# Copyright 2018 The OpenSSL Project Authors. All Rights Reserved.
+#
+# Licensed under the OpenSSL license (the "License").  You may not use
+# this file except in compliance with the License.  You can obtain a copy
+# in the file LICENSE in the source distribution or at
+# https://www.openssl.org/source/license.html
 
 HERE=`dirname $0`