I'm trying to create a NuGet package from a VS 2017 project that contains a reference to a 3rd party DLL (Kendo.mvc.dll).  No matter what I try, I can't get nuget pack to automatically include that DLL in my NuGet package's lib folder.  
I originally created the .nuspec file from the command line with the command nuget spec [project's name and path].csproj.  I then tweaked the settings of that file which resulted in this .nuspec file:
<?xml version="1.0"?>
<package >
  <metadata>
    <id>$id$</id>
    <version>$version$</version>
    <title>$title$</title>
    <authors>our names</authors>
    <owners>$author$</owners>
    <requireLicenseAcceptance>false</requireLicenseAcceptance>
    <description>the description</description>
    <releaseNotes>First release</releaseNotes>
    <copyright>Copyright 2018</copyright>
    <tags>entity-framework-6 mvc5</tags>
  </metadata>
</package>
I then used nuget pack to create the package, which resulted in this:
From what I've read in the documentation (MS Docs - Creating NuGet packages) I was expecting nuget pack to automatically include any non-nuget-sourced DLLs referenced in the project in the package, but that's not happening?
I've tried the following to see if it makes any difference, all to no avail:
- Adding a 
libfolder to the root of my project and putting the DLL in there (and experimented a bit with changing the Build Action and Copy to Output Directory settings). That created a lib folder under the Content folder in the NuGet package, rather than adding the DLL to the samelibfolder that contains the assembly's DLL. I did that because the MS docs talk about a convention based file structure. - Referencing the DLL from a folder in C:\Program Files and setting the Copy Local property for the DLL to true in the Properties
 
This question talks about adding a separate element for the 3rd party DLL which I'm guessing refers to adding the files explicitly in the .nuspec file before generating the package, e.g.
  <files>
    <file src="bin\Debug\Kendo.Mvc.???" target="lib\net461" />
  </files>
That does work, but shouldn't this be added automatically if it's needed when generating a .nuspec file from a csproj file?

