Docs should suggest installing vscode-styled-components for VS Code support

[tchajed]

Description: In VS Code, you can install the vscode-styled-components extension to get syntax highlighting for CSS within css`...` templates. This isn't obviously the right extension to use but it's very helpful for writing code, so I'd recommend mentioning it in the installation instructions.

Documentation links:

https://emotion.sh/docs/install is probably the right place to put this.