Merge #742: Backport 0.21.0 release note updates

b7d5959 Backport 0.21.0 release note updates (azuchi)

Pull request description:

ACKs for top commit:
  MarcoFalke:
    ACK b7d5959
  harding:
    ACK b7d5959 , thanks!

Tree-SHA512: 039c89fc21fdd1ed24147f43339f95ee6cf2ef7ad8947d8e28826febe1e244a879c58e285f4b017abda1d7695b0fb2d46383335a87294d3612bdc5bbc0ed5ecd

Author: harding

_releases/0.21.0.md

@@ -125,7 +125,7 @@ P2P and network changes
 - This release adds support for serving
   [BIP157](https://github.com/bitcoin/bips/blob/master/bip-0157.mediawiki) compact
   filters to peers on the network when enabled using
-  `-blockfilterindex=1 -peercfilters=1`. (#16442)
+  `-blockfilterindex=1 -peerblockfilters=1`. (#16442)
 
 - This release adds support for signets
   ([BIP325](https://github.com/bitcoin/bips/blob/master/bip-0325.mediawiki)) in