Fix 0.12 release notes on block relaying

The previous information about block relaying in pruned mode suggested
that blocks are relayed only to nodes that support BIP 130, which is not
true.

Author: KrzysiekJ

doc/release-notes/release-notes-0.12.0.md

@@ -104,9 +104,6 @@ announcing their headers directly, instead of just announcing the hash. In a
 reorganization, all new headers are sent, instead of just the new tip. This
 can often prevent an extra roundtrip before the actual block is downloaded.
 
-With this change, pruning nodes are now able to relay new blocks to compatible
-peers.
-
 Memory pool limiting
 --------------------
 
@@ -188,6 +185,14 @@ the OP_RETURN. The limit on OP_RETURN output size is now applied to the entire
 serialized scriptPubKey, 83 bytes by default. (the previous 80 byte default plus
 three bytes overhead)
 
+Relay: New and only new blocks relayed when pruning
+---------------------------------------------------
+
+When running in pruned mode, the client will now relay new blocks. When
+responding to the `getblocks` message, only hashes of blocks that are on disk
+and are likely to remain there for some reasonable time window (1 hour) will be
+returned (previously all relevant hashes were returned).
+
 Relay and Mining: Priority transactions
 ---------------------------------------
 
@@ -887,4 +892,3 @@ Thanks to everyone who directly contributed to this release:
 - zathras-crypto
 
 As well as everyone that helped translating on [Transifex](https://www.transifex.com/projects/p/bitcoin/).
-