[ImgBot] Optimize images (#8)

*Total -- 282.95kb -> 245.95kb (13.07%)

/assets/5.png -- 19.46kb -> 6.72kb (65.47%)
/assets/2.png -- 7.48kb -> 5.33kb (28.82%)
/assets/3.png -- 17.40kb -> 12.41kb (28.67%)
/assets/4.png -- 15.75kb -> 11.35kb (27.91%)
/assets/1.png -- 11.72kb -> 8.50kb (27.45%)
/assets/6.gif -- 20.77kb -> 17.64kb (15.1%)
/assets/usage.png -- 190.37kb -> 184.01kb (3.34%)

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

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