Add contributing doc (#825)
Add contributing doc (#825)


chrisdunelm/google-api-dotnet-client,Duikmeester/google-api-dotnet-client,googleapis/google-api-dotnet-client,jskeet/google-api-dotnet-client,googleapis/google-api-dotnet-client,Duikmeester/google-api-dotnet-client,googleapis/google-api-dotnet-client,chrisdunelm/google-api-dotnet-client,Duikmeester/google-api-dotnet-client,jskeet/google-api-dotnet-client,Duikmeester/google-api-dotnet-client,chrisdunelm/google-api-dotnet-client,chrisdunelm/google-api-dotnet-client,jskeet/google-api-dotnet-client