dotnet restore docs don't include information about --interactive switch

[matthiaswenz]

Issue description

dotnet restore documentation does not include information about --interactive switch.
Somebody told me to use dotnet restore --interactive and it didn't work on .NET Core 2.1.3xx because the switch was not known back then, when I installed 2.1.403, it worked, but I don't see this flag mentioned in the documentation.

According to the command line help this switch does:

--interactive - Allows the command to stop and wait for user input or action (for example to complete authentication).

If this is the only thing that needs to be added to the documentation, I'll happily file a PR for this. I didn't find any previous issues mentioning this.

Target framework

• .NET Core (2.1.4xx)
• .NET Framework
• .NET Standard

If using the .NET Core SDK, include dotnet --info output. If using .NET Framework without the .NET Core SDK, include info from Visual Studio's Help > About Microsoft Visual Studio dialog.

dotnet --info output or About VS info

.NET Core SDK (reflecting any global.json):
 Version:   2.1.403
 Commit:    04e15494b6

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  10.14
 OS Platform: Darwin
 RID:         osx-x64
 Base Path:   /usr/local/share/dotnet/sdk/2.1.403/

Host (useful for support):
  Version: 2.1.5
  Commit:  290303f510

.NET Core SDKs installed:
  2.1.202 [/usr/local/share/dotnet/sdk]
  2.1.302 [/usr/local/share/dotnet/sdk]
  2.1.403 [/usr/local/share/dotnet/sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.2 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.5 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.2 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.5 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.0.9 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.2 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.4 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

[Thraka]

@ranterle I think this sounds like a good one to do. @mairaw Any reason why @ranterle shouldn't handle this one?