When creating Visual studio Tools addins for D365 Fin ops you would need to copy it into the extension folder. This folder is most probably different on every machine.
To get the folder Open Regedit and navigate to: HKCU:\SOFTWARE\Microsoft\VisualStudio\14.0\ExtensionManager\EnabledExtensions
This stores the folder under the property DynamicsRainer*
Store your addin over here.
I have a powershell script that copies all the dll’s into that folder