Some additional info to the sync doc

docs/sync.markdown

@@ -26,3 +26,7 b' performed.'
 The node signs the data with its key. The receiving node saves the key at the
 first sync and checks it every time. If the key has changed, the info won't be
 saved from the node (or the node id must be changed).
+
+Each node holds a list of networks it wants to get info from.
+
+Each post has an ID in the unique format: node-id/post-id