Merge bitcoin/bitcoin#26920: doc: add release note for #25957 (fast wallet rescan)

783288334c doc: add release note for #25957 (fast wallet rescan) (Sebastian Falbesoner)

Pull request description:

  This PR adds a missing release note for #25957.

ACKs for top commit:
  Sjors:
    ACK 783288334c

Tree-SHA512: 817aa3d27b3f839de3975ace7c8ec59bcc4dbe4b5628bf64153e503cd143599d8923bd7e181ad5b196dacf1a9078347825bc40d4de5c6e2df9ed12e752217094

doc/release-notes-25957.md

@@ -0,0 +1,9 @@
+Wallet
+------
+
+- Rescans for descriptor wallets are now significantly faster if compact
+  block filters (BIP158) are available. Since those are not constructed
+  by default, the configuration option "-blockfilterindex=1" has to be
+  provided to take advantage of the optimization. This improves the
+  performance of the RPC calls `rescanblockchain`, `importdescriptors`
+  and `restorewallet`. (#25957)