docs(radio-button): add a bit of padding to radio button example (#7433)

src/material-examples/radio-overview/radio-overview-example.css

@@ -1 +1,3 @@
-/** No CSS for this example */
+.mat-radio-button ~ .mat-radio-button {
+  padding-right: 16px;
+}

src/material-examples/radio-overview/radio-overview-example.ts

@@ -6,5 +6,6 @@ import {Component} from '@angular/core';
 @Component({
   selector: 'radio-overview-example',
   templateUrl: 'radio-overview-example.html',
+  styleUrls: ['radio-overview-example.css'],
 })
 export class RadioOverviewExample {}