Update README install directions for v0.7

[samuela]

Was previously showing outdated install directions for v0.5.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: samuela
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[k8s-ci-robot]

Hi @samuela. Thanks for your PR.

I'm waiting for a bazelbuild member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[chases2]

/ok-to-test