Building helloworld-from-cli dotnetcore sample failing from command line

[simonz130]

This is what I get when building according to the instructions here:
https://grpc.io/docs/quickstart/csharp.html
(look for "Build the example" section, then Using .NET Core SDK from the command line

C:\dev\grpc\examples\csharp\helloworld-from-cli>dotnet build **/project.json
Microsoft (R) Build Engine version 15.7.177.53362 for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

MSBUILD : error MSB1009: Project file does not exist.
Switch: **/project.json