Docs: Outdated Cargo features in README

[Musab1258]

The Cargo features documented in the README.md are currently out of sync with the actual features defined in Cargo.toml. This causes build errors for contributors/users following the instructions.

Specifically:

• The README lists kyoto as a blockchain client option, but the actual flag is cbf. Running cargo build --features kyoto fails.
• The README lists sp as the feature for silent payments, but the actual flag is silent-payments. Running cargo build --features sp fails.

I am already working on a fix for this and will be opening a PR shortly to update the README to match the current Cargo.toml.