portico: Mention about thirdparty desktop apps.

static/js/portico/landing-page.js

@@ -127,6 +127,7 @@ var apps_events = function () {
 
     var update_page = function () {
         var $download_instructions = $(".download-instructions");
+        var $third_party_apps = $("#third-party-apps");
         var version_info = info[version];
 
         $(".info .platform").text(version_info.alt);
@@ -140,6 +141,13 @@ var apps_events = function () {
         } else {
             $download_instructions.hide();
         }
+
+        if (version === "mac" || version === "windows" || version === "linux") {
+            $third_party_apps.show();
+        } else {
+            $third_party_apps.hide();
+        }
+
     };
 
     $(window).on('popstate', function () {

static/styles/portico.css

@@ -2158,3 +2158,8 @@ input.new-organization-button {
 .portico-page.error .portico-page-container {
     padding: 0;
 }
+
+#third-party-apps {
+    margin-top: 20px;
+    padding-right: 10px;
+}

templates/zerver/apps.html

@@ -58,6 +58,12 @@
                 <i class="icon fa fa-mobile-phone" data-label="iOS"></i>
             </a>
         </div>
+        <div id="third-party-apps">
+            Zulip also works great in pinned browser tabs and
+            multi-protocol desktop chat apps
+            like <a href="http://rambox.pro">Rambox</a>
+            and <a href="https://meetfranz.com">Franz</a>.
+        </div>
     </div>
 </div>
 {% endblock %}