This can be used to set a custom text for the license if it can't be set via adw.about_window.AboutWindow.licenseType.
When set, adw.about_window.AboutWindow.licenseType will be set to gtk.types.License.Custom.
The license text will be displayed on the Legal page, below the copyright information.
License text can contain Pango markup and links.
adw.about_window.AboutWindow.addLegalSection can be used to add license information for the application dependencies or other components.