mason/dhandler: Add a `license' relationship to the AGPL link.

There's also a `license' relation on the Creative Commons link in my
custom footer.  Let's hope this isn't too confusing.

diff --git a/mason/dhandler b/mason/dhandler
index 813e637..24b5026 100755 (executable)
--- a/mason/dhandler
+++ b/mason/dhandler
@@ -288,7 +288,7 @@ Failed to find &lsquo;<% $path |h %>&rsquo;.
     Trivial Gallery, copyright &copy; 2021 Mark Wooding.
     Free software: you can modify it and/or redistribute it under the
     terms of the
-    <a href="https://www.gnu.org/licenses/agpl-3.0.en.html">GNU Affero
+    <a rel=license href="https://www.gnu.org/licenses/agpl-3.0.en.html">GNU Affero
     General Public License version 3</a>.
     Browse or download
     the <a href="https://git.distorted.org.uk/~mdw/tgal/">source code</a>.