Add content to readme file

Author: davidnguyen11

README.md

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 # Priority Queue
 
-[![codecov](https://codecov.io/gh/davidnguyen179/priority-queue/branch/master/graph/badge.svg)](https://codecov.io/gh/davidnguyen179/priority-queue) [![Build Status](https://travis-ci.org/davidnguyen179/priority-queue.svg?branch=master)](https://travis-ci.org/davidnguyen179/priority-queue) [![PRs Welcome](https://img.shields.io/badge/PRs-welcome-brightgreen.svg?style=flat-square)](https://github.com/davidnguyen179/priority-queue/pulls) [![License: MIT](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/davidnguyen179/priority-queue/blob/master/LICENSE)
+A priority queue is a collection in which items can be added at any time, but the only item that can be removed is the one with the highest priority.
+
+For more information, please check [wiki](https://en.wikipedia.org/wiki/Priority_queue).
+
+[![codecov](https://codecov.io/gh/davidnguyen179/priority-queue/branch/master/graph/badge.svg)](https://codecov.io/gh/davidnguyen179/priority-queue) [![Build Status](https://travis-ci.org/davidnguyen179/priority-queue.svg?branch=master)](https://travis-ci.org/davidnguyen179/priority-queue) [![PRs Welcome](https://img.shields.io/badge/PRs-welcome-brightgreen.svg?style=flat-square)](https://github.com/davidnguyen179/priority-queue/pulls) [![License: MIT](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/davidnguyen179/priority-queue/blob/master/LICENSE)
+
+## Motivation
+
+During practising some challenges in `leetcode`. I found this [problem](https://leetcode.com/problems/last-stone-weight/) requires `priority queue`. So I decided to research some documentations online and try to implement by myself this lib. The result beats 97% in `leetcode`.
+
+## Usage
+
+The `priority queue` lib uses max heap as a default way to build a queue.
+
+**Max priority queue**
+
+_with array of numbers_
+
+```ts
+const p = new PriorityQueue();
+p.push(2);
+p.push(7);
+p.push(4);
+p.push(1);
+p.push(8);
+p.push(1);
+
+// The queue: [8, 7, 4, 1, 2, 1]
+```
+
+_with array of objects_
+
+```ts
+const p = new PriorityQueue(function (a, b) {
+  return a.value < b.value;
+});
+
+p.push({ text: "a", value: 2 });
+p.push({ text: "b", value: 7 });
+p.push({ text: "c", value: 4 });
+p.push({ text: "d", value: 1 });
+p.push({ text: "e", value: 8 });
+p.push({ text: "f", value: 1 });
+
+/** The queue
+[
+  { text: 'e', value: 8 },
+  { text: 'b', value: 7 },
+  { text: 'c', value: 4 },
+  { text: 'd', value: 1 },
+  { text: 'a', value: 2 },
+  { text: 'f', value: 1 },
+]
+ */
+```
+
+If you want to support min `priority queue`. The lib allows providing the customized `comparator`.
+
+**Min priority queue**
+
+_with array of numbers_
+
+```ts
+const p = new PriorityQueue(function (a, b) {
+  return a > b;
+});
+p.push(2);
+p.push(7);
+p.push(4);
+p.push(1);
+p.push(8);
+p.push(1);
+
+// The queue: [1, 2, 1, 7, 8, 4]
+```
+
+_with array of objects_
+
+```ts
+const p = new PriorityQueue(function (a, b) {
+  return a.value > b.value;
+});
+
+p.push({ text: "a", value: 2 });
+p.push({ text: "b", value: 7 });
+p.push({ text: "c", value: 4 });
+p.push({ text: "d", value: 1 });
+p.push({ text: "e", value: 8 });
+p.push({ text: "f", value: 1 });
+
+/** The queue
+[
+  { text: 'd', value: 1 },
+  { text: 'a', value: 2 },
+  { text: 'f', value: 1 },
+  { text: 'b', value: 7 },
+  { text: 'e', value: 8 },
+  { text: 'c', value: 4 }
+]
+ */
+```
+
+## API
+
+### push(value)
+
+Add elements to queue
+
+```ts
+const p = new PriorityQueue();
+p.push(1); // adding "1" to queue
+p.push(2); // adding "2" to queue
+p.push(3); // adding "3" to queue
+
+// The queue: [3, 1, 2]
+```
+
+### pop
+
+Extract the largest or smallest element from the queue
+
+```ts
+const p = new PriorityQueue();
+p.push(1); // adding "1" to queue
+p.push(2); // adding "2" to queue
+p.push(3); // adding "3" to queue
+
+const elmenet = p.pop(); // Output: 3
+```
+
+The queue looks like this `[2, 1]`
+
+### top
+
+Peek the element (get the largest or smallest element without removing it from queue)
+
+```ts
+const p = new PriorityQueue();
+p.push(1); // adding "1" to queue
+p.push(2); // adding "2" to queue
+p.push(3); // adding "3" to queue
+
+const elmenet = p.pop(); // Output: 3
+
+// The queue is remained the same
+```
+
+### size
+
+Get the size of the queue
+
+```ts
+const p = new PriorityQueue();
+p.push(1); // adding "1" to queue
+p.push(2); // adding "2" to queue
+p.push(3); // adding "3" to queue
+p.push(4); // adding "4" to queue
+
+const length = p.size(); // Output: 4
+```
+
+### empty
+
+Check whether the queue is empty or not.
+
+- true: if the queue is empty
+- false: if the queue has data
+
+### toArray
+
+Extract queue to array
+
+```ts
+const p = new PriorityQueue();
+p.push(1); // adding "1" to queue
+p.push(2); // adding "2" to queue
+p.push(3); // adding "3" to queue
+
+const array = p.toArray(); // Output: [3, 1, 2]
+```
+
+## Running time
+
+| Operation | Binary heap |
+| --------- | ----------- |
+| push      | O(lg n)     |
+| top       | O(1)        |
+| pop       | O(lg n)     |