Update SchemaController.js

Author: dblythy

src/Controllers/SchemaController.js

@@ -150,6 +150,7 @@ const defaultColumns: { [string]: SchemaFields } = Object.freeze({
   },
 });
 
+// fields required for read or write operations on their respective classes.
 const requiredColumns = Object.freeze({
   read: {
     _User: ['username'],
@@ -160,7 +161,6 @@ const requiredColumns = Object.freeze({
   }
 });
 
-
 const invalidColumns = ['length'];
 
 const systemClasses = Object.freeze([