Add Liu Hui to README.

Author: trekhleb

README.md

@@ -53,6 +53,7 @@ a set of rules that precisely define a sequence of operations.
   * [Integer Partition](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/math/integer-partition)
   * [Sieve of Eratosthenes](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/math/sieve-of-eratosthenes) - finding all prime numbers up to any given limit
   * [Is Power of Two](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/math/is-power-of-two) - check if the number is power of two (naive and bitwise algorithms)
+  * [Liu Hui π Algorithm](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/math/liu-hui) - approximate π calculations based on N-gons.
 * **Sets**
   * [Cartesian Product](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/sets/cartesian-product) - product of multiple sets
   * [Power Set](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/sets/power-set) - all subsets of a set