Updating documentation

[georgewrmarshall]

Description

This PR updates the documentation for the design tokens to provide better usage and explanations for

• README
• Introduction
• Color introduction
• Brand colors
• Theme colors

The main updates include:

• Updating deprecated storybook components such as ComponentStory, ComponentMeta
• • Updates storybook files to Component Story Format 3.0 (CSF3)
• Improving documentation focusing on usage and the why

Screenshots/Screencasts

Before

https://github.com/MetaMask/design-tokens/assets/8112138/afab07c9-63d2-4122-85db-c0c1c1befccd

After

https://github.com/MetaMask/design-tokens/assets/8112138/05213710-aa10-4a79-9ec4-2b6e040852f5

Manual testing steps

1. Go to the latest storybook build of this PR
2. Read through pages listed above
3. Check they make sense and that stories are working correctly

[metamaskbot]

Builds ready [28944fe]

Storybook: Storybook

[metamaskbot]

Builds ready [7c0223c]

Storybook: Storybook

[metamaskbot]

Builds ready [ed53249]

Storybook: Storybook

[metamaskbot]

Builds ready [ec3cd2e]

Storybook: Storybook

[metamaskbot]

Builds ready [c2c8e48]

Storybook: Storybook

[metamaskbot]

Builds ready [8fa3991]

Storybook: Storybook

[metamaskbot]

Builds ready [c95bad4]

Storybook: Storybook

[metamaskbot]

Builds ready [31bec54]

Storybook: Storybook

[metamaskbot]

Builds ready [aa83d99]

Storybook: Storybook