Add driver override to envvars.rst
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6911>
diff --git a/docs/envvars.rst b/docs/envvars.rst
index fa414bd..2395406 100644
--- a/docs/envvars.rst
+++ b/docs/envvars.rst
@@ -180,6 +180,8 @@
instance version as advertised by ``vkEnumerateInstanceVersion``
- This can be very useful for debugging but some features may not be
implemented correctly. (For developers only)
+``MESA_LOADER_DRIVER_OVERRIDE``
+ chooses a different driver binary such as ``etnaviv`` or ``zink``.
NIR passes environment variables
--------------------------------
