[docs] Add mui-treasury as extra resources for inspiration

[siriwatknp]

Summary

mui-treasury/layout tutorial just released a few days ago and had a chat with @oliviertassinari to add it as related projects. One more I think we can add link to Card section in mui-treasury for other developers to see an example of customization.

Here is what I will do for this issue

• add mui-treasury/layout tutorial to related project
• add link to mui-treasury/card

• I have searched the issues of this repository and believe that this is not a duplicate.

[oliviertassinari]

👑 If you are looking for inspiration, you can check MUI Treasury's customization examples.

@siriwatknp We link mui-treasury after a couple of customization demos. For instance here: https://material-ui.com/components/buttons/#customized-buttons. What do you think of increasing the cover of this approach to as many components as possible? :)

add mui-treasury/layout tutorial to related project

This sounds great. I think that we can add a new "Layout" subsection under https://material-ui.com/discover-more/related-projects/#components 💯.

[siriwatknp]

@oliviertassinari that sounds great!