doc: add disk space requirement note to release notes

Mention that BIP157 block filters require approximately 1GB+ of
additional disk space, as suggested in code review.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: PastaPastaPasta

doc/release-notes-6711.md

@@ -4,5 +4,6 @@ Updated settings
 - BIP157 compact block filters are now automatically enabled for masternodes. This improves privacy for light clients
   connecting to masternodes and enables better support for pruned nodes. When a node is configured as a masternode
   (via `-masternodeblsprivkey`), both `-peerblockfilters` and `-blockfilterindex=basic` are automatically enabled.
+  Note that this feature requires approximately 1GB+ of additional disk space for the block filter index.
   Regular nodes keep the previous defaults (disabled). Masternodes can still explicitly disable these features
   if needed by setting `-peerblockfilters=0` or `-blockfilterindex=0` (#6711).