Update the launch file to work with modern joy. (backport #52)

[mergify]

It should use "device_id" (not "dev") as the parameter, and the parameter should be a number, not a path (this is effectively the SDL device number, which is cross-platform).

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This is an automatic backport of pull request #52 done by Mergify.

[mergify]

Cherry-pick of e4856e4 has failed:

On branch mergify/bp/iron/pr-52
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Changes to be committed:
	modified:   launch/teleop-launch.py

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

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