docs(radio): Add README.

Closes #182

Author: Michael Lin

src/components/radio/README.md

@@ -0,0 +1,52 @@
+# MdRadio
+Radio buttons allow the user to select one option from a set. Use radio buttons for exclusive selection if you think that the user needs to see all available options side-by-side.
+
+![Preview](https://material.angularjs.org/material2_assets/radio/radios.png)
+
+### Examples
+A basic radio group would have the following markup.
+```html
+<md-radio-group>
+  <md-radio-button value="option_1">1</md-radio-button>
+  <md-radio-button value="option_2">2</md-radio-button>
+</md-radio-group>
+```
+
+A dynamic example, populated from a `data` variable:
+```html
+<md-radio-group [(value)]="groupValue">
+  <md-radio-button *ngFor="#d of data" [value]="d.value">
+    {{d.label}}
+  </md-radio-button>
+</md-radio-group>
+```
+
+## `<md-radio-group>`
+### Properties
+
+| Name | Type | Description |
+| --- | --- | --- |
+| `selected` | `MdRadioButton` | The currently selected button. |
+| `value` | `any` | The current value for this group. |
+| `disabled` | `boolean` | Whether the group is disabled. |
+
+When selection is changed, an event is emitted from the `change` EventEmitter property.
+
+### Notes
+The `md-radio-group` component has no button initially selected.
+
+## `<md-radio-button>`
+### Properties
+
+| Name | Type | Description |
+| --- | --- | --- |
+| `id` | `string` | The unique ID of this radio button. |
+| `name` | `string` | Group name, defaults to parent radio group if present. |
+| `value` | `any` | The value of this radio button. |
+| `checked` | `boolean` | Whether the radio is checked. |
+| `disabled` | `boolean` | Whether the radio is disabled. |
+
+When checked, an event is emitted from the `change` EventEmitter property.
+
+### Notes
+* The `md-radio-button` component by default uses the accent color from the theme palette.