Improved documentation for FormBuilderCustomField

Author: danvick

README.md

@@ -185,7 +185,10 @@ In order to create an input field in the form, along with the label, and any app
 | `valueTransformer` | `ValueTransformer<T>` | `null` | `false` | Function that transforms field value before saving to form value. e.g. transform TextField value for numeric field from `String` to `num` |
 The rest of the attributes will be determined by the type of Widget being used.
 
-### Building your own custom `FormField`
+### Building your own custom field
+To build your own field within a `FormBuilder`, we use `FormBuilderCustomField` which will require that you define your own `FormField`.
+The `FormField` will not require a `validator` if the `validators` property is already defined in the `FormBuilderCustomField`.
+
 ```dart
 FormBuilderCustomField(
   attribute: "name",

lib/src/form_builder_custom_field.dart

@@ -2,9 +2,20 @@ import 'package:flutter/material.dart';
 import 'package:flutter_form_builder/flutter_form_builder.dart';
 
 class FormBuilderCustomField<T> extends StatefulWidget {
+  /// Identifier for the field input.
+  ///
+  /// Used as a key to final map returned when the form is submitted
   final String attribute;
+
+  /// The [FormField] widget that will house the custom input
   final FormField<T> formField;
+
+  /// An optional list of [FormFieldValidator]s that validates the input in the field.
   final List<FormFieldValidator> validators;
+
+  /// Called before field value is submitted.
+  ///
+  /// Can be used to convert the value to the output expected by the user.
   final ValueTransformer valueTransformer;
 
   FormBuilderCustomField({