better readme

README.md

@@ -14,3 +14,60 @@ npm install concurrent-task --save
 ```
 
 ## Usage
+
+Below is an example of 5 tasks with 2 steps to execute for each.
+
+```js
+  const concurrent('concurrent-task')
+
+  // create a task runner with concurrency limit 2
+  const runner = concurrent(2)
+
+  runner.set({
+    steps: {
+      step1: {
+        timeout: 1000,
+        tryCount: 2,
+        run (data, resolve, reject) {
+          return clearTimeout.bind(null, setTimeout(() => {
+            return data.success.compute() ? resolve() : reject(new Error('some error'))
+          }, data.seconds * 1000))
+        }
+      },
+      step2: {
+        timeout: 500,
+        tryCount: 3,
+        run (data, resolve, reject) {
+          return clearTimeout.bind(null, setTimeout(() => {
+            return data.success.compute() ? resolve() : reject(new Error('some error'))
+          }, data.seconds * 1000))
+        }
+      }
+    },
+    tasks: {
+      task1: { seconds: 0.3, success: true },
+      task2: { seconds: 0.7, success: true },
+      task3: { seconds: 0.2, success: false },
+      task4: { seconds: 1.2, success: false },
+      task5: { seconds: 0.3, success: true }
+    }
+  })
+
+  runner
+    .on('error', (key, error) => {
+      // one of tasks had an error on one of steps
+      // key is key of task
+    })
+    .on('task-done', key => {
+      // one of tasks completed all steps with no error
+    })
+    .on('complete', () => {
+      // all the tasks completed all steps
+      // if any of them had errors
+      // tryCounts are exhausted
+
+      // log runner status
+      console.log(runner.status())
+    })
+    .run()
+```