You can add a "Notes" section to a user's profile using a custom text-type question in the User Form. Follow the steps below.
Navigate to User Forms and click on the "All Users" user group. Click Add Question and choose Create New Question.
Select "Text" from the Question Type field and enter "Notes" into the Name and Prompt fields.
Select "Only to administrators" from the To whom is this question and its answer visible? drop-down menu and "Only administrators" from the Who is allowed to change the answer to this question? drop-down menu.
Select "Multi Line" from the Text Mode drop-down menu.
Click on the Save button to save your changes. You will now be able to enter details into your "Notes" field in any user's profile, but volunteers will not be able to see or edit that field or its contents.