Family trees can look great with or without a text decal, so it's purely a matter of preference whether you include one or not. If you want to add one, here's how.
To start with click the "Text Decal" icon in the left sidebar to open the text decal sidebar panel. Once in the panel, you can add whatever heading and/or subheading text you like by typing in their respective text boxes in the panel. Changes are updated in real time.
Font, font size, spacing, and color are controlled independently between the heading and the subheading, so you can customize any way you'd like without being unduly constrained. to change the font color, simply click on the color swatch and either use the color picker or enter a Hex or RGB value.
To change the font size or margin (space between the heading or subheading and the chart), simply click and drag the corresponding slider. Font is chosen using the drop-down menu under heading or subheading respectively.
There are lots of different options for what text to actually use as your text decal. Some classic options include "The [Your Last Name] Family", "Genealogy", "My Family Tree", "Family", or "Ancestors". For more suggestions, check out this blog post.
What text decal would you put on your chart?