DOC: prepear documentation interface change

Author: Isan-Rivkin

SPEC/PUBSUB.md

@@ -2,6 +2,7 @@
 
 * [pubsub.subscribe](#pubsubsubscribe)
 * [pubsub.unsubscribe](#pubsubunsubscribe)
+* [pubsub.unsubscribeAll](#pubsubunsubscribeall)
 * [pubsub.publish](#pubsubpublish)
 * [pubsub.ls](#pubsubls)
 * [pubsub.peers](#pubsubpeers)
@@ -82,6 +83,46 @@ ipfs.pubsub.subscribe(topic, receiveMsg, (err) => {
 })
 ```
 
+#### `pubsub.unsubscribeAll`
+
+> Unsubscribes from a pubsub topic.
+
+##### Go **WIP**
+
+##### JavaScript - `ipfs.pubsub.unsubscribe(topic, handler, [callback])`
+
+- `topic: String` - The topic to unsubscribe from
+- `callback: (Error) => {}` (Optional) Called once the unsubscribe is done.
+
+If no `callback` is passed, a [promise][] is returned.
+
+This works like `EventEmitter.removeAllListeners`, The underlying subscription will only be canceled once all listeners for a topic have been removed.
+
+**Example:**
+
+```JavaScript
+const topic = 'fruit-of-the-day'
+
+ipfs.pubsub.subscribe(topic, (msg) => console.log(msg.toString()), (err) => {
+  if (err) {
+    return console.error(`failed to subscribe to ${topic}`, err)
+  }
+
+  console.log(`subscribed to ${topic}`)
+
+  // unsubscribe a second later
+  setTimeout(() => {
+    ipfs.pubsub.unsubscribeAll(topic,(err) => {
+      if (err) {
+        return console.error(`failed to unsubscribe from ${topic}`, err)
+      }
+
+      console.log(`unsubscribed from ${topic}`)
+    })
+  }, 1000)
+})
+```
+
 A great source of [examples][] can be found in the tests for this API.
 
 #### `pubsub.publish`