Document managed-queue, tinker and skills:install commands in README

[usamamuneerchaudhary]

adds the ten shipped-but-undocumented commands to the README command reference:

• A new Managed queues section covering managed-queue:create, pause, resume, purge, set-default, failed-jobs, retry-failed-job and delete-failed-job, with a short note on the non-interactive options create accepts and which commands take --force.
• cloud tinker and cloud skills:install added to the Other table, with a one-line note each on --code / --timeout and --global / --project / --agent.

All ten commands are public (none are hidden) and each is already in the CHANGELOG, managed queues in #164, tinker in #141 / #142, skills:install in #143, but none appear anywhere in the README. Someone reading the command reference has no way to discover them.

Notes

• Descriptions are taken from each command's $description.
• Option names come from the command signatures.
• Docs only, no code changes.

[joetannenbaum]

Thank you!