Add Brick\Math

README.md

 ### Numbers
 *Libraries for working with numbers.*
 
+* [Brick\Math](https://github.com/brick/math) - A library providing large number support: `BigInteger`, `BigDecimal` and `BigRational`.
 * [ByteUnits](https://github.com/gabrielelana/byte-units) - A library to parse, format and convert byte units in binary and metric systems.
 * [LibPhoneNumber for PHP](https://github.com/giggsey/libphonenumber-for-php) - A PHP implementation of Google's phone number handling library.
 * [PHP Conversion](https://github.com/Crisu83/php-conversion) - Another library for converting between units of measure.