A description can be added to a requirement version. In the requirement details window, navigate to the Versions tab and make sure you are in the correct version using the dropdown in the top left corner of the details window. Note that only versions in draft mode can be edited by the requirement owner and those added as a contributor to the version.
Click Edit in the top left corner of the description area. Changes are saved in real-time and can be edited by multiple users simultaneously. Click the Done button to exit the editing mode.
Users will need to be added as contributors to the requirement, and have project permissions set to view and edit in the requirements module. Depending on the settings of the user's project permissions, they may be able to view all the project requirements or just a subset of them. Users added to a specific requirement as a contributor or reviewer will be able to view it.