add CC0 to valid licences (json)

Author: Moth-Tolias

views/package_format_json.dt

@@ -190,6 +190,7 @@ block body
 		|<code>BSL-1.0</code> (Boost Software License),
 		|<code>BSD 2-clause</code>,
 		|<code>BSD 3-clause</code>,
+		|<code>CC0</code> (Creative Commons Zero),
 		|<code>EPL-1.0</code> (Eclipse Public License),
 		|<code>GPL-2.0</code>,
 		|<code>GPL-3.0</code>,