Fix broken link to robot_setup in README (backport #1263)

[mergify]

The respective URCap installation setup got merged into the robot_setup in the client_library's documentation.

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This is an automatic backport of pull request #1263 done by Mergify.

[mergify]

Cherry-pick of d7f3ea7 has failed:

On branch mergify/bp/humble/pr-1263
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit d7f3ea7.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   README.md

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[urfeex]

The Humble README actually points to the Humble docs, which are still structured with the separated instructions, hence closing this.