Fix copyright
Fix copyright

> Since this is a copy-and-paste of old text, I think the copyright year should match when the original text was written, which according to git was 2017.

Co-Authored-By: turt2live <f36f6a6abc4b55589c96c71fceedf83e596b8f33@gmail.com>
matrix-org/matrix-doc,matrix-org/matrix-doc,matrix-org/matrix-doc,matrix-org/matrix-doc