Add TODO comments from review

eth/p2p/discoveryv5/protocol.nim

@@ -363,6 +363,8 @@ proc revalidateLoop(p: Protocol) {.async.} =
       await sleepAsync(rand(10 * 1000).milliseconds)
       let n = p.routingTable.nodeToRevalidate()
       if not n.isNil:
+        # TODO: Should we do these in parallel and/or async to be certain of how
+        # often nodes are revalidated?
         await p.revalidateNode(n)
   except CancelledError:
     trace "revalidateLoop canceled"

eth/p2p/discoveryv5/routing_table.nim

@@ -239,6 +239,7 @@ proc randomNodes*(r: RoutingTable, count: int): seq[Node] =
   # insignificant compared to the time it takes for the network roundtrips when connecting
   # to nodes.
   while len(seen) < count:
+    # TODO: Is it important to get a better random source for these sample calls?
     let bucket = sample(r.buckets)
     if bucket.nodes.len != 0:
       let node = sample(bucket.nodes)