[backport#16063] rpc: Mention getwalletinfo where a rescan is triggered

Summary:
rpc: Mention getwalletinfo where a rescan is triggered (João Barbosa)

Backport of Core PR16063

Test Plan:

ninja

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D7367