Add temporary "unimplemented" Register box

src/qml/Pages/AddAccount/AddAccount.qml

@@ -9,7 +9,7 @@ HPage {
         ]
 
         SignIn { Component.onCompleted: forceActiveFocus() }
-        Item {}  // TODO
-        Item {}  // TODO
+        Register {}
+        Recovery {}
     }
 }

src/qml/Pages/AddAccount/Register.qml

@@ -0,0 +1,29 @@
+import QtQuick 2.12
+import QtQuick.Layouts 1.12
+import "../../Base"
+
+HBox {
+    id: signInBox
+    clickButtonOnEnter: "ok"
+
+    buttonModel: [
+        { name: "ok", text: qsTr("Register from Riot"), iconName: "register" },
+    ]
+
+    buttonCallbacks: ({
+        ok: button => {
+            Qt.openUrlExternally("https://riot.im/app/#/register")
+        }
+    })
+
+
+    HLabel {
+        wrapMode: Text.Wrap
+        text: qsTr(
+            "Registering is not implemented yet. You can create a new " +
+            "account from a client that supports it, such as Riot."
+        )
+
+        Layout.fillWidth: true
+    }
+}