docs/zink: document rgtc requirement
OpenGL 3.0 requires RGTC support, and until we have emulation in place, we should document that requirement.
Fixes: d50e8554 ("zink: add feature-documentation")
OpenGL 3.0 requires RGTC support, and until we have emulation in place, we should document that requirement.
Fixes: d50e8554 ("zink: add feature-documentation")