Update README.md to move the PSVM link under a "Tooling" section under the "Releases" section (#4734)

This update implements the suggestion from @Kianenigma mentioned in
https://github.com/paritytech/polkadot-sdk/pull/4718#issuecomment-2153777367

Replaces the "Other useful resources and tooling" section at the bottom
with a new (nicer) "Tooling" section just under the "Releases" section.