Finish the initial requirements for the header partial

module/data/Actor/Geist.mjs

@@ -1,3 +1,18 @@
 import { EntityData } from "./Entity.mjs";
 
-export class GeistData extends EntityData {};
+const { fields } = foundry.data;
+
+export class GeistData extends EntityData {
+	static defineSchema() {
+		const schema = super.defineSchema();
+
+		schema.description = new fields.HTMLField({
+			blank: true,
+			nullable: true,
+			trim: true,
+			initial: null,
+		});
+
+		return schema;
+	};
+};