VSIX extension - How can I ensure a referenced dll or assembly is included in the VSIX file?

I found a solution to this problem, and I can see the dll now included in the VSIX and a user confirmed that it works for him.

1. In Visual Studio, with the extension solution open,
2. double click the .vsixmanifest file
3. Open the "Assets" tab
4. Click "New"
5. Set Type to "Microsoft.VisualStudio.Assembly"
6. Set Source to "A File on FileSystem"
7. Click Browse to set Path to your dll, (don't worry the reference is not added as an absolute path, but added as a relative path or just a strong assembly name)
8. You can leave "Embed in this folder" empty.
9. Click OK
10. Rebuild the solution, and the file should be in the VSIX file now.

This line is then added to the vsixmanifest file:

<Asset Type="Microsoft.VisualStudio.Assembly" d:Source="File" Path="Microsoft.CodeAnalysis.CSharp.dll" AssemblyName="Microsoft.CodeAnalysis.CSharp, Version=1.2.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />