Add steps to update copyrights

This was written down in the outdated doc/dev/release documentation.
Since the rest of that file can go, add these steps to a separate file
and update it to current standards (e.g. use git commands).

doc/dev/copyrights

@@ -0,0 +1,16 @@
+#
+# Merge and Update copyrights
+#
+
+git clean -dfx
+perl util/merge_copyrights
+diff util/copyrights util/newcopyrights
+... examine output, particularly any files with the "?" type, and
+... then edit util/newcopyrights if necessary
+$ mv util/newcopyrights util/copyrights
+$ perl util/update_copyrights < util/copyrights
+$ git diff
+... examine output, edit as necessary.  mail me about anything that
+... the script should have been able to do itself. :-)
+$ git add util/copyrights
+$ git commit -m 'update_copyrights'