Add links to the Pin API (#140)

Author: enricomarino

README.md

@@ -120,7 +120,10 @@ In order to be considered "valid", an IPFS core implementation  must expose the
     - [`object.patch.rmLink`](/API/object#objectpatchrmlink)
     - [`object.patch.appendData`](/API/object#objectpatchappenddata)
     - [`object.patch.setData`](/API/object#objectpatchsetdata)
-- [pin (not spec'ed yet)](/API/pin)
+- [pin](/API/pin)
+  - [`pin.add`](/API/pin#add)
+  - [`pin.ls`](/API/pin#ls)
+  - [`pin.rm`](/API/pin#rm)
 - [pubsub](/API/pubsub)
   - [`pubsub.subscribe`](/API/pubsub#pubsubsubscribe)
   - [`pubsub.unsubscribe`](/API/pubsub#pubsubunsubscribe)