README.md needs to be updated

[osamuaoki]

Hi,

Thank you for the slick UI design.

I like ability to set count down timer or alarm clock quickly via keyboard.

But I am a bit confused about UI. Look at attached image. The UI design has changed. See the menu and the README.md page.

Please consider updating the linked images in README.md

Also, it will be nice if you rewrite README.md to start it with short summary of this plugin instead of talking about its predecessor. For example:

Kitchen Timer Extension provides:
* Countdown Timer: Select countdown timer via GUI choice or with text such as "10:00" for ten minutes.
* Alarm Clock: Set and activate alarm clock with text such as "@10:00" for 10:00 AM.
These can be activated immediately (Quick mode) or preset mode.
You can create preset GUI selection entries for these countdown time and alarm clock.

This plug in is based on now unmaintained [Gnome shell kitchen timer extension](https://extensions.gnome.org/extension/3955/kitchen-timer/) with the ability to run multiple simultaneous timers.

The configuration panel seems to be buggy and loses preset values when it hit some buggy parts. This could be GNOME version issue. At least I couldn't figure out ... I also don't see menu for Persistent mode. It will be nice PERSISTENCE can be configured also by this panel. Also, does preset menu aware of PERSISTENCE? These are few points I noticed.