windows: Update the docs for env vars
We've replaced some env vars with a new one.
Update the docs to match.
diff --git a/docs/reference/gtk/windows.md b/docs/reference/gtk/windows.md
index 886b99f..96fa5e6 100644
--- a/docs/reference/gtk/windows.md
+++ b/docs/reference/gtk/windows.md
@@ -14,14 +14,19 @@
The Win32 GDK backend can be influenced with some additional environment
variables.
-### GDK_IGNORE_WINTAB
+### GDK_WIN32_TABLET_INPUT_API
-If this variable is set, GTK doesn't use the Wintab API for tablet support.
+If this variable is set, it determines the API that GTK uses for tablet support.
+The possible values are:
-### GDK_USE_WINTAB
+`none`
+: Disables tablet support
-If this variable is set, GTK uses the Wintab API for tablet support.
-This is the default.
+`wintab`
+: Use the Wintab API
+
+`winpointer`
+: Use the Windows Pointer Input Stack API. This is the default.
## Windows-specific handling of cursors