[ImgBot] Optimize images

*Total -- 790.32kb -> 701.48kb (11.24%)

/public/assets/images/background/sliderbg.jpg -- 33.75kb -> 16.72kb (50.47%)
/screenshot.png -- 555.34kb -> 488.79kb (11.98%)
/.github/screnshot.png -- 201.23kb -> 195.97kb (2.61%)

Signed-off-by: ImgBotApp <ImgBotHelp@gmail.com>

Author: ImgBotApp