Jan (Beulich) ran into this, and indeed I could not find it documented. So I added it. ;-)
Applied. Gerald --- svnwrite.html.orig 2015-04-06 20:15:18.000000000 +0800 +++ svnwrite.html 2015-12-22 17:07:33.636074381 +0800 @@ -420,6 +420,10 @@ ssh <i>username</i>@gcc.gnu.org email mynewaddr...@example.com </pre></blockquote> +<p>Similarly if you want to add a new SSH key to your account:</p> +<blockquote><pre> +ssh <i>username</i>@gcc.gnu.org append-key < KEYFILE +</pre></blockquote> </body> </html>