Resize image in readme

[lyndaidaii]

Summary of the changes (in less than 80 characters):

max-width: 100%
means: maximum width in percent of the readme block

If the content is larger than the maximum width, it will automatically change the height of the element.
If the content is smaller than the maximum width, the max-width property has no effect.

before resize:

after resize:

Addresses #8502

[skofman1]

Missing screenshot?

[zhhyu]

What will it look like when reflowing to a smaller device?

[lyndaidaii]

What will it look like when reflowing to a smaller device?

it will auto adjust the image size based on the readme container. means it will become smaller when it reflowing to a smaller device. I did test by making browser smaller, it looks good.