chore(nit): update per feedback

Author: amcdnl

src/lib/tabs/tab-content.ts

@@ -1,6 +1,6 @@
 import {Directive, TemplateRef} from '@angular/core';
 
-@Directive({ selector: '[mdTabContent]' })
+@Directive({selector: '[mdTabContent]'})
 export class MdTabContent {
   constructor(public template: TemplateRef<any>) { }
 }

src/lib/tabs/tab-group.spec.ts

@@ -418,7 +418,7 @@ describe('lazy loaded tabs', () => {
     TestBed.compileComponents();
   }));
 
-  it('should lazy load the second tab', (done) => {
+  it('should lazy load the second tab', async () => {
     let fixture = TestBed.createComponent(TemplateTabs);
     fixture.detectChanges();
 
@@ -430,7 +430,6 @@ describe('lazy loaded tabs', () => {
       fixture.detectChanges();
       let child = fixture.debugElement.query(By.css('.child'));
       expect(child.nativeElement).toBeDefined();
-      done();
     });
   });
 });

src/lib/tabs/tabs.md

@@ -92,3 +92,28 @@ Tabs without text or labels should be given a meaningful label via `aria-label`
 | `LEFT_ARROW`         | Move focus to previous tab |
 | `RIGHT_ARROW`        | Move focus to next tab     |
 | `SPACE` or 'ENTER'   | Switch to focused tab      |
+
+
+## Lazy Loading
+By default, the tab contents are eagerly loaded. Eagerly loaded tabs
+will initalize the child components but not inject them into the DOM
+until the tab is activated.
+
+If the tab contains several complex child components, it is advised
+to lazy load the tab's content. Tab contents can be lazy loaded by
+declaring the body in a `ng-template` with the `mdTabContent` attribute.
+
+```html
+<md-tab-group>
+  <md-tab label="First">
+    <ng-template mdTabContent>
+      The First Content
+    </ng-template>
+  </md-tab>
+  <md-tab label="Second">
+    <ng-template mdTabContent>
+      The Second Content
+    </ng-template>
+  </md-tab>
+</md-tab-group>
+```