[docs] Broken size links

[oliviertassinari]

• This is not a v0.x issue.
• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior 🤔

The links in the documentation are working.

Current Behavior 😯

We mention the bundle size in the following files:

• /docs/src/pages/system/basics/basics.md -> link bundlephobia.com, ok
• /docs/src/pages/demos/drawers/drawers.md -> link nothing, empirical statement, hum
• /docs/src/pages/customization/css-in-js/css-in-js.md -> link nothing, empirical statement, hum
• /docs/src/pages/utils/popper/popper.md -> link .size-limit.js, broken
• /docs/src/pages/layout/use-media-query/use-media-query.md -> link .size-limit.js, broken
• /docs/src/pages/guides/minimizing-bundle-size/minimizing-bundle-size.md link .size-limit.js, broken

Steps to Reproduce 🕹

Navigate to https://next.material-ui.com.

Context 🔦

The links were broken with #14587.

Your Environment 🌎

Tech	Version
Material-UI	v4.0.0-alpha.1