Add Copyright section

since this is a recurring theme
and it is good to have a place like this to point people to

timestamp/copyright/README.md

@@ -0,0 +1,24 @@
+Some software and documentation uses the year of build
+in copyright strings.
+
+As long as this only touches comments in .c or .h files,
+it will only alter the build-id in the resulting binary.
+
+However, building today's software in 2037 and getting a
+`Copyright © 2002-2037 THEAUTHORS`
+is wrong, because nobody authored anything in 2037 in this version.
+
+Projects are better off manually updating the year with git commits
+or updating the date from a ChangeLog or input file mtime
+so it remains constant for release tarballs.
+
+See also on the [stackoverflow discussion](https://stackoverflow.com/questions/2390230/do-copyright-dates-need-to-be-updated) titled "Do copyright dates need to be updated?"
+
+Seen in the wild:
+* https://github.com/dealii/dealii/pull/7258/files cmake
+* https://gitlab.com/gnutls/gnutls/merge_requests/928/diffs autoconf/shell
+* https://github.com/kubernetes/kubernetes/pull/59172/files go
+* https://github.com/pytest-dev/pytest/pull/3710/files python
+* https://github.com/apache/cassandra/commit/84fc68ce3f77e88a542dd2443e560cb291109198 java
+* https://issues.apache.org/jira/browse/MCOMPILER-380 java
+* https://www.redhat.com/archives/libguestfs/2018-August/msg00230.html