add facebook

_config.yml

@@ -25,6 +25,10 @@ social:
         title:  Twitter
         handle: bigchaindb
         url:    https://twitter.com/bigchaindb
+    facebook:
+        title:  Facebook
+        handle: bigchaindb
+        url:    https://www.facebook.com/BigchainDB/
     medium:
         title:  Blog
         url:    https://blog.bigchaindb.com

_src/_data/menus.yml

@@ -28,6 +28,8 @@ community:
       url: https://github.com/bigchaindb
     - title: Twitter
       url: https://twitter.com/BigchainDB
+    - title: Facebook
+      url: https://www.facebook.com/BigchainDB/
     - title: Meetup
       url: https://www.meetup.com/BigchainDB-IPDB-Meetup