Merge #636: Add compact block diagram detail explanation.

1a5f5cb Add compact block diagram detail explanation. (Carl Dong)

Pull request description:

Tree-SHA512: 84facebe5eedf7176797db6ed158129abc0e9f779ce93d718c20aa72cc458cb57b96a01ba6e89dc97b5340d77fa2ca5897b9f3e102f5229dc0e1f0432cec5773

Author: harding

_posts/en/posts/2016-06-07-compact-blocks-faq.md

@@ -31,7 +31,7 @@ The advantage of this approach is that transactions only need to be sent once in
 
 In addition, the compact block relay proposal also provides a second mode of operation (called *high bandwidth mode*) where the receiving node asks a few of its peers to send new blocks directly without asking for permission first, which may increase bandwidth (because two peers may try sending the same block at the same time) but which further reduces the amount of time it takes blocks to arrive (latency) on high-bandwidth connections.
 
-The diagram below shows the way nodes currently send blocks compared to compact block relay's two operating modes.
+The diagram below shows the way nodes currently send blocks compared to compact block relay's two operating modes. The grey box on node A's timeline represents the period in which it is performing validation.
 
 ![Compact Blocks diagram](https://raw.githubusercontent.com/bitcoin/bips/master/bip-0152/protocol-flow.png)