Synfig version & platform:
1.3.16 on Ubuntun 18.04 (via AppImage)

Issue description:

I was perusing the dev. docs, looking through the parts about the rendering engine: https://synfig-docs-dev.readthedocs.io/en/latest/common/structure.html#render-engine

In there it states there is an OpenGL backend, versus the default enabled one is a software one called Cobra. Is there a way that I can enable the OpenGL one? I've found it a bit of a pain how slow it can be to preview my animations. What I'd love is way to see my edits' results in realtime. I'm wondering if the OpenGL backend can do this for me.

When I went to change my WorkArea render in the Preferences, I only saw the software renders available. Do I need to clone the repo myself and build my own Synfig studio?