Update Wallet.md

[arshbot]

Updates wallet.md to add Sparrow among the list of wallets we recognize to allow gap-limit config

Tackles https://github.com/btcpayserver/btcpayserver-doc/issues/1295

[pavlenex]

Thanks for a PR @arshbot, since then I discovered there are several more:

• Bitcoin Core
• Sparrow
• Specter https://specter.solutions/index.html
• Nunchuk https://nunchuk.io/
• Samourai wallet (when used with Dojo Maintenance Tool)

Let's list them all and link accordingly?

[arshbot]

@pavlenex done!