Add docs example of custom timezone with MomentDateAdapter

#### Bug, feature request, or proposal:
[X] Feature Request

#### What is the expected behavior?
MomentDateAdapter should have timezone support.
Moment has a timezone lib (http://momentjs.com/timezone/) which you can set the timezone
manually. This is needed when you want to create a common date/datetime based in a specific timezone.

#### What is the current behavior?
MomentDateAdapter supports browser's timezone only when creating a new date moment object.

#### What are the steps to reproduce?
* Include MatMomentDateModule to use MomentDateAdapter
* Create a mat-datepicker
* Console the output (date generated)

#### What is the use-case or motivation for changing an existing behavior?
I do want to create a common date/datetime based in a specific timezone.

#### Which versions of Angular, Material, OS, TypeScript, browsers are affected?
Angular CLI: 1.5.0
Node: 8.8.1
OS: darwin x64
Angular: 5.0.1
... animations, common, compiler, compiler-cli, core, forms
... http, platform-browser, platform-browser-dynamic
... platform-server, router

`@angular/cdk: 5.0.0-rc0`
`@angular/cli: 1.5.0`
`@angular/flex-layout: 2.0.0-beta.10-4905443`
`@angular/material-moment-adapter: 5.0.0-rc0`
`@angular/material: 5.0.0-rc0`
`@angular-devkit/build-optimizer: 0.0.32`
`@angular-devkit/core: 0.0.20`
`@angular-devkit/schematics: 0.0.34`
`@ngtools/json-schema: 1.1.0`
`@ngtools/webpack: 1.8.0`
`@schematics/angular: 0.1.2`
`typescript: 2.4.2`
`webpack-sources: 1.0.1`
`webpack: 3.8.1`

まず MatMomentDateModule と MomentDateAdapter に関する現在のドキュメントを読み、その後、issue に記載されているタイムゾーンのシナリオを確認します。手動で選択したタイムゾーンの日付または日時を作成する方法を示すドキュメント例を追加し、その例がアダプターの現在の動作と一致することを確認します。

索引モデルが issue の本文から書いたものです。