[ADF-1586] Added doc files for Form library (#2503)

* [ADF-1586] Added docs for Form library

* [ADF-1586] Added updated doc index

docs/widget.component.md

@@ -0,0 +1,38 @@
+# Widget component
+
+Base class for standard and custom widget classes.
+
+## Basic Usage
+
+```ts
+import { Component } from '@angular/core';
+import { WidgetComponent } from 'ng2-activiti-form';
+
+@Component({
+    selector: 'custom-editor',
+    template: `
+        <div style="color: red">Look, I'm a custom editor!</div>
+    `
+})
+export class CustomEditorComponent extends WidgetComponent {}
+```
+
+### Properties
+
+| Name | Type | Default | Description |
+| --- | --- | --- | --- |
+| readOnly | boolean | false | Does the widget show a read-only value? (ie, can't be edited) |
+| field | [FormFieldModel](form-field.model.md) |  | Data to be displayed in the field |
+
+## Details
+
+The Widget component is the base class for all standard and custom form widgets. See the
+[Form Extensibility and Customisation](extensibility.md) page for full details about
+implementing custom widgets.
+
+<!-- Don't edit the See also section. Edit seeAlsoGraph.json and run config/generateSeeAlso.js -->
+<!-- seealso start -->
+## See also
+
+- [Extensibility](extensibility.md)
+<!-- seealso end -->