doc: getdeploymentinfo release notes tweaks

Author: ajtowns

doc/release-notes-23508.md

@@ -115,6 +115,15 @@ Updated RPCs
 New RPCs
 --------
 
+- Information on soft fork status has been moved from `getblockchaininfo`
+  to the new `getdeploymentinfo` RPC which allows querying soft fork status at any
+  block, rather than just at the chain tip. Inclusion of soft fork
+  status in `getblockchaininfo` can currently be restored using the
+  configuration `-deprecatedrpc=softforks`, but this will be removed in
+  a future release. Note that in either case, the `status` field
+  now reflects the status of the current block rather than the next
+  block. (#23508)
+
 Build System
 ------------