Added NuGet install instructions to docs

Closes #17214.

README.md

@@ -32,6 +32,7 @@ Several quick start options are available:
 - Install with [npm](https://www.npmjs.com): `npm install bootstrap`.
 - Install with [Meteor](https://www.meteor.com): `meteor add twbs:bootstrap`.
 - Install with [Composer](https://getcomposer.org): `composer require twbs/bootstrap`.
+- Install with [NuGet](https://www.nuget.org): CSS: `Install-Package bootstrap -Pre` Sass: `Install-Package bootstrap.sass -Pre` (`-Pre` is only required until Bootstrap v4 has a stable release).
 
 Read the [Getting started page](http://getbootstrap.com/getting-started/) for information on the framework contents, templates and examples, and more.
 

docs/getting-started/download.md

@@ -69,6 +69,16 @@ You can also install and manage Bootstrap's Sass and JavaScript using [Composer]
 $ composer require twbs/bootstrap
 {% endhighlight %}
 
+### NuGet
+
+If you develop in .NET, you can also install and manage Bootstrap's [CSS](https://www.nuget.org/packages/bootstrap/) or [Sass](https://www.nuget.org/packages/bootstrap.sass/) and JavaScript using [NuGet](https://www.nuget.org):
+
+{% highlight powershell %}
+PM> Install-Package bootstrap -Pre
+PM> Install-Package bootstrap.sass -Pre
+{% endhighlight %}
+
+The `-Pre` is required until Bootstrap v4 has a stable release.
 
 ## Custom builds