Describe `output` parameter in run_in_windows_bash

[taoyouh]

This adds document for PR https://github.com/conan-io/conan/pull/11306

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}