Move comments from README

Example
```javascript
/**
* Gets the first element of `array`.
*
* @category Array
* @param {Array} array The array to query.
* @returns {*} Returns the first element of `array`.
* @example
*
* head(['foo', 'bar'])
* // => 'foo'
*
* head([])
* // => undefined
*/
const head = arr => arr[0]
```

- [ ] array.mjs
- [ ] decorators.mjs
- [x] math.mjs
- [ ] object.mjs

Start by reviewing the comment example in the README and the documentation already present in math.mjs. Then inspect array.mjs, decorators.mjs, and object.mjs, moving the relevant comments into those files until the unchecked checklist items are complete.

Written by the indexing model from the issue text.