How to you get the "Share with Google Drive" contextual menu option in Finder?
You need to enable the Finder extension Google Drive. 

Open the contextual menu for any file, and click on Share and then More. 



That will bring you to the Extensions window. 

Click on Finder and in the "Select extensions for customizing Finder" select Google Drive. 



Now you should see the "View in Google Drive" and "Share with Google Drive" options when you Control-click / secondary click on files inside your Google Drive.