Clarify ownership when creating a document in a team drive

> Creating an owned document in your team's drive will give ownership to the team.

This applies to the new "store in" picker on the creation screen as well as other cases. Add to https://docs.cryptpad.org/en/user_guide/apps/general.html#new-document under "Owned".

Open the user guide page at docs.cryptpad.org/en/user_guide/apps/general.html and locate the “New document” section, specifically “Owned.” Add the clarification that creating an owned document in a team drive gives ownership to the team, covering the new “store in” picker and other cases. Done means the ownership behavior is clearly documented in that section.

Written by the indexing model from the issue text.