Multiline strings

I searched "line feed", "multi", "line" and found nothing. Also in verbatim string ("@") documentation page I didn't find anything about line feeds in strings.

---
#### Document Details

⚠ *Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.*

* ID: 7eb81599-a548-5d41-4013-812d9148b09d
* Version Independent ID: de28387f-e401-9ecd-1fc0-a9e37d55d6ea
* Content: [String Class (System)](https://docs.microsoft.com/en-us/dotnet/api/system.string?view=netframework-4.7.2)
* Content Source: [xml/System/String.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System/String.xml)
* Product: **dotnet-api**
* GitHub Login: @rpetrusha
* Microsoft Alias: **ronpet**