Missing documentation for part of our theme

### Describe the feature you'd like

Our theme offers values for multiple aspects of Web development but they are not documented so our users cannot easily know about them, it would be nice to properly document all of these values to ease the life of developers using Wave

This is our theme
```tsx
const theme: DefaultTheme = {
breakpoints: Breakpoints,
fontSizes: ['0.75rem', '0.875rem', '1rem', '1.25rem', '1.5rem', '2rem', '2.5rem', '3rem'],
// fontSizes also has `small` = fontSizes[1], `medium` = fontSizes[2] and `large` = 1.125rem
fontWeights: {
normal: 400,
semibold: 600,
bold: 700
},
fonts: {
normal: fontStack(['Open Sans', 'sans-serif']),
monospace: fontStack(['Hack', 'monospace'])
},
mediaQueries: MediaQueries,
space: Spaces,
radii: ['0rem', '0.125rem', '0.25rem', '0.5rem'],
iconSizes: {
small: 12,
medium: 24,
large: 28
},
shadows: {
small: '0 0.0625rem 0.25rem 0 rgba(0,0,0,0.1)',
medium: '0 0 0.5rem 0.1875rem rgba(0,0,0,0.08)',
large: '0 0 0.75rem 0.25rem rgba(0,0,0,0.12)'
}
};
```

Currently only `breakpoints`, `mediaQueries` and `spaces` are documented, the rest is missing 😅

### Describe alternatives you've considered

I don't see alternatives, not documenting these values leads to developers either having to search through the source code to find our theme or directly not using our theme and resorting to custom values instead, I believe we should avoid that