Put simply, a Pattern Library unifies a production team and a Styleguide unifies an organization. A Pattern Library is a tool often used by developers and designers to unify around building project components - good examples of these are Storybook and Pattern Lab. A Styleguide can include components from the Pattern Library but also includes other information useful to other teams such as content editors, user experience, accessibility and executives. A good example of a Styleguide is Carbon Design System.
A Design System combines a Styleguide and a Pattern Library (see above). It is both the workshop and the storefront.
We are aiming for early 2020 for the full beta release of the Emulsify Design System that will include the Styleguide. You can get started now with the alpha which is a full replacement of the old Emulsify and the Styleguide can be added seamlessly later!