It's not always obvious how mockgen-generated code has been created,
particularly when coming to it without prior knowledge of it. Good practice
would be to include a go:generate directive that can be used to regenerate
the code, but that's not always done.

Currently the comments on the generated code look something like this:

// Code generated by MockGen. DO NOT EDIT.
// Source: github.com/foo/bar (interfaces: Baz)

// Package mocks is a generated GoMock package.

I propose something along the lines of this:

// Code generated by MockGen. DO NOT EDIT.
// Source: github.com/foo/bar (interfaces: Baz)
//
// Generated by this command:
//    gomock github.com/foo/bar Baz

// Package mocks is a generated GoMock package.