[Console] Add Process Helper documentation
feature #3756 [WCM][Console] Add Process Helper documentation (romainneutron)

This PR was merged into the master branch.

Discussion
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[WCM][Console] Add Process Helper documentation

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | yes (symfony/symfony#10627)
| Applies to    | 2.5+
| Fixed tickets | n/a

Commits
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1705231 [Console] Add Process Helper documentation