docs(overlay): mention including overlay css (#992)

* docs(overlay): mention including overlay css

* add to readmes

Author: jelbourn

GETTING_STARTED.md

@@ -123,6 +123,16 @@ Import the components in your application module:
 - [Puppy Love Mobile (Google IO 2016)](https://github.com/kara/puppy-love-io)
 
 
+### Additional setup for `md-menu` and `md-tooltip`:
+For alpha.7, you need to include the overlay styles in your app via a `link` element. This will
+look something like
+```html
+<link href="vendor/@angular2-material/core/overlay/overlay.css" rel="stylesheet">
+```
+
+In future releases, all of the core styles will be combined into a single distributed css file.
+
+
 ### Additional setup for `md-slide-toggle` and `md-slider`:
 The slide-toggle and slider components have a dependency on [HammerJS](http://hammerjs.github.io/).
 1) Add HammerJS to your application via [npm](https://www.npmjs.com/package/hammerjs), a CDN 

src/components/menu/README.md

@@ -27,6 +27,12 @@ import {MdMenuModule} from '@angular2-material/menu';
 export class MyAppModule {}
 ```
 
+For alpha.7, you need to include the overlay styles in your app via a `link` element. This will
+look something like
+```html
+<link href="vendor/@angular2-material/core/overlay/overlay.css" rel="stylesheet">
+```
+
 ### Simple menu
 
 In your template, create an `md-menu` element. You can use either `<button>` or `<anchor>` tags for 

src/components/tooltip/README.md

@@ -1,6 +1,14 @@
 # MdTooltip
 Tooltip allows the user to specify text to be displayed when the mouse hover over an element.
 
+### Setup
+For alpha.7, you need to include the overlay styles in your app via a `link` element. This will
+look something like
+```html
+<link href="vendor/@angular2-material/core/overlay/overlay.css" rel="stylesheet">
+```
+
+
 ### Examples
 A button with a tooltip
 ```html