Add a note to use the desktop builds when seshat isn't available

Fixes https://github.com/vector-im/element-web/issues/15184

This is currently temporary design for https://github.com/vector-im/element-web/issues/12896 but does not fix it.

res/css/_components.scss

@@ -100,6 +100,7 @@
 @import "./views/elements/_AccessibleButton.scss";
 @import "./views/elements/_AddressSelector.scss";
 @import "./views/elements/_AddressTile.scss";
+@import "./views/elements/_DesktopBuildsNotice.scss";
 @import "./views/elements/_DirectorySearchBox.scss";
 @import "./views/elements/_Dropdown.scss";
 @import "./views/elements/_EditableItemList.scss";

res/css/views/elements/_DesktopBuildsNotice.scss

@@ -0,0 +1,28 @@
+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+.mx_DesktopBuildsNotice {
+    text-align: center;
+    padding: 0 16px;
+
+    > * {
+        vertical-align: middle;
+    }
+
+    > img {
+        margin-right: 8px;
+    }
+}

res/css/views/rooms/_SearchBar.scss

@@ -68,3 +68,4 @@ limitations under the License.
         cursor: pointer;
     }
 }
+