discv4: fix definition of node k-bucket distances (#212)

Author: jacktan1

discv4.md

@@ -31,9 +31,9 @@ from the response.
 ## Kademlia Table
 
 Nodes in the Discovery Protocol keep information about other nodes in their neighborhood.
-Neighbor nodes are stored in a routing table consisting of 'k-buckets'. For each `0 ≤ i <
-256`, every node keeps a k-bucket for nodes of distance between `2i` and `2i+1` from
-itself.
+Neighbor nodes are stored in a routing table consisting of 'k-buckets'. For each `i` in
+`0 ≤ i < 256`, every node keeps a k-bucket of neighbors with distance
+`2^i ≤ distance < 2^(i+1)` from itself.
 
 The Node Discovery Protocol uses `k = 16`, i.e. every k-bucket contains up to 16 node
 entries. The entries are sorted by time last seen — least-recently seen node at the head,