runtime(doc): improve suggested detection method for WSL

Current method can't work in Windows Terminal as far as I know.

This is a way that already had been adopted in `dist/vim9.vim`.

closes: #20714

Signed-off-by: Mao-Yining <mao.yining@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

diff --git a/runtime/doc/os_win32.txt b/runtime/doc/os_win32.txt
index 694e0fe75ca468e264250f34728469b125328f5f..666f265ec94ec5f016f4aa44b038a9a4aa614853 100644 (file)
--- a/runtime/doc/os_win32.txt
+++ b/runtime/doc/os_win32.txt
@@ -1,4 +1,4 @@
-*os_win32.txt* For Vim version 9.2.  Last change: 2026 Feb 14
+*os_win32.txt* For Vim version 9.2.  Last change: 2026 Jul 22
 
 
                  VIM REFERENCE MANUAL    by George Reilly
@@ -48,7 +48,7 @@ For compiling see "src/INSTALLpc.txt".                        *win32-compiling*
                                                        *WSL*
 When using Vim on WSL (Windows Subsystem for Linux) the remarks here do not
 apply, `has('win32')` will return false then.  In case you need to know
-whether Vim is running on WSL you can use `exists('$WSLENV')`.
+whether Vim is running on WSL you can use `exists('$WSL_DISTRO_NAME')`.
 
 ==============================================================================
 1. Known problems                                      *win32-problems*