[README] fix broken wiki link

[macfarla]

PR description

Fixed Issue(s)

This page https://wiki.hyperledger.org/display/BESU/Hyperledger+Besu is now https://wiki.hyperledger.org/display/BESU/Besu - I've asked for a redirect to be setup as well but for now it's a broken link

Thanks for sending a pull request! Have you done the following?

• Checked out our contribution guidelines?
• Considered documentation and added the doc-change-required label to this PR if updates are required.
• Considered the changelog and included an update if required.
• For database changes (e.g. KeyValueSegmentIdentifier) considered compatibility and performed forwards and backwards compatibility tests

Locally, you can run these tests to catch failures early:

• unit tests: ./gradlew build
• acceptance tests: ./gradlew acceptanceTest
• integration tests: ./gradlew integrationTest
• reference tests: ./gradlew ethereum:referenceTests:referenceTests

[cdivitotawela]

LGTM