add temporary key bindings to move up/down by screen row

src/gui/Window.cc

@@ -358,6 +358,12 @@ void Window::handle_keyval(uint32_t keyval)
             case 'I':
                 m_focused_buffer_pane->enter_insert_mode(EnterInsertModeMode::START_OF_LINE);
                 break;
+            case 'J':
+                m_focused_buffer_pane->cursor_move(BufferPane::CursorMovement::SCREEN_ROW_DOWN);
+                break;
+            case 'K':
+                m_focused_buffer_pane->cursor_move(BufferPane::CursorMovement::SCREEN_ROW_UP);
+                break;
             case 'O':
                 m_focused_buffer_pane->enter_insert_mode(EnterInsertModeMode::NEW_LINE_BEFORE);
                 break;