docs: update pubsub func signatures

Author: daviddias

README.md

@@ -413,8 +413,8 @@ The core API is grouped into several areas:
 - [dht (not implemented, yet!)](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/)
 
 - [pubsub](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md)
-  - [`ipfs.pubsub.subscribe(topic, options, handler, callback)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubsubscribe)
-  - [`ipfs.pubsub.unsubscribe(topic, handler)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubunsubscribe)
+  - [`ipfs.pubsub.subscribe(topic, handler, options, callback)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubsubscribe)
+  - [`ipfs.pubsub.unsubscribe(topic, handler, callback)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubunsubscribe)
   - [`ipfs.pubsub.publish(topic, data, callback)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubpublish)
   - [`ipfs.pubsub.ls(topic, callback)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubls)
   - [`ipfs.pubsub.peers(topic, callback)`](https://github.com/ipfs/interface-ipfs-core/tree/master/SPEC/PUBSUB.md#pubsubpeers)