Merge #19802: doc: elaborate on release notes wrt netmasks

8de51d1513 doc: elaborate on release notes wrt netmasks (Vasil Dimov)

Pull request description:

  doc: elaborate on release notes wrt netmasks

  A minor followup from https://github.com/bitcoin/bitcoin/pull/19628#issuecomment-679958713.

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  practicalswift:
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Tree-SHA512: ccece7c3057e476d59e9996582e8594b3db9eaed397139217335a41307e542194c8d13ad72458eaa8580a5c469fef9cc9e3f11c1c609617757579530b465e5b0

doc/release-notes.md

@@ -155,7 +155,8 @@ Updated settings
 
 - Netmasks that contain 1-bits after 0-bits (the 1-bits are not contiguous on
   the left side, e.g. 255.0.255.255) are no longer accepted. They are invalid
-  according to RFC 4632.
+  according to RFC 4632. Netmasks are used in the `-rpcallowip` and `-whitelist`
+  configuration options and in the `setban` RPC. (#19628)
 
 Changes to Wallet or GUI related settings can be found in the GUI or Wallet  section below.