Document the API URI

Change-Id: I6d8d11723e38b5587fdc820780a2e686d4025625
diff --git a/templates/doc/api.html.ep b/templates/doc/api.html.ep
index 4aaacf2..a7f1a30 100644
--- a/templates/doc/api.html.ep
+++ b/templates/doc/api.html.ep
@@ -7,3 +7,9 @@
   All API endpoints either use KoralQuery or are (more or lest) REST-ful web APIs.</p>
 
 <p>All publicly available API endpoints including their requests and responses are described in the <%= ext_link_to 'GitHub Wiki', "https://github.com/KorAP/Kustvakt/wiki" %> of <%= embedded_link_to 'doc', 'Kustvakt', 'korap', 'kustvakt' %>.</p>
+
+% if (app->config('Kalamar')->{experimental_proxy}) {
+%   my $api_url = $c->url_for('proxy' => (apiv => $Kalamar::API_VERSION))->to_abs->scheme('https');
+%   $api_url->path->trailing_slash(1);
+<p>The root service can be found at <code id="api-service-uri"><%=  $api_url %></code>.</p>
+% }