I followed the getting started instructions and the "generate step definitions" is missing from context menu.
I tried adding the additional specflow packages from nuget for mstest and still nothing.
I had the same problem. I was looking for this option in contextual menu of the feature file, but this option exists in the contextual menu of the content of the feature file. So, try open the feature file (*.feature) in the Visual Studio text editor and click right button of the mouse inside text editor. Example of the file:
Scenario: Add two numbers
Given I have entered 50 into the calculator
And I have entered 70 into the calculator
When I press add
Then the result should be 120 on the screen