docs: add ToC link to pubsub.unsubscribe

Author: Alan Shaw

doc/API.md

@@ -7,11 +7,11 @@
   * [`stop`](#stop)
   * [`dial`](#dial)
   * [`dialProtocol`](#dialprotocol)
-  * [`hangUp`](#hangUp)
+  * [`hangUp`](#hangup)
   * [`handle`](#handle)
   * [`unhandle`](#unhandle)
   * [`ping`](#ping)
-  * [`peerRouting.findPeer`](#peerRoutingfindPeer)
+  * [`peerRouting.findPeer`](#peerroutingfindpeer)
   * [`contentRouting.findProviders`](#contentroutingfindproviders)
   * [`contentRouting.provide`](#contentroutingprovide)
   * [`contentRouting.put`](#contentroutingput)
@@ -21,6 +21,7 @@
   * [`pubsub.getTopics`](#pubsubgettopics)
   * [`pubsub.publish`](#pubsubpublish)
   * [`pubsub.subscribe`](#pubsubsubscribe)
+  * [`pubsub.unsubscribe`](#pubsubunsubscribe)
   * [`metrics.global`](#metricsglobal)
   * [`metrics.peers`](#metricspeers)
   * [`metrics.protocols`](#metricsprotocols)