Add docs for using NuGet on macOS

doc/user/packages/nuget_repository/index.md

@@ -18,7 +18,7 @@ NuGet CLI is probably already installed.
 
 Alternatively, you can use [.NET SDK 3.0 or later](https://dotnet.microsoft.com/download/dotnet-core/3.0), which installs NuGet CLI.
 
-You can confirm that [nuget CLI](https://www.nuget.org/) is properly installed with:
+You can confirm that [NuGet CLI](https://www.nuget.org/) is properly installed with:
 
 ```shell
 nuget help
@@ -36,6 +36,18 @@ Available commands:
 [output truncated]
 ```
 
+### macOS support
+
+For macOS, you can also use [Mono](https://www.mono-project.com/) to run
+the NuGet CLI. For Homebrew users, run `brew install mono` to install
+Mono. Then you should be able to download the Windows C# binary
+`nuget.exe` from the [NuGet CLI page](https://www.nuget.org/downloads)
+and run:
+
+```shell
+mono nuget.exe
+```
+
 ## Enabling the NuGet Repository
 
 NOTE: **Note:**