We frequently use string fields when instructions or definitions are needed to improve data quality in our system. Below is a sample from our Risk object configuration that includes definitions for the different risk categories.
In the object layout, you can set the field as a Text Area and then define the width/height of the cell. When you create the string field, enter a default value, mark the field read-only, and populate null values with the default once the narrative has been agreed upon. Making a future change to the information displayed in read-only field can be tedious so make sure there is agreement on the final language and proof-read it BEFORE populating null values with the default.