correct the directory mount point rule again

Mount-on-Windows.md

@@ -21,10 +21,10 @@ weed.exe mount -filer=127.0.0.1:8888 -dir=S:
 The mount point is one of:
 
 * a **drive letter**, `S:`, which must be free
-* a **directory**, `C:\seaweed\data` — either an empty one, or one that does not exist yet and whose parent does
+* a **directory that does not exist yet**, `C:\seaweed\data` — its parent must exist
 * a **UNC path**, `\\seaweedfs\data`
 
-A directory mount point becomes a reparse point for as long as the mount lasts, and NTFS only allows that on an empty directory, so a populated one is rejected. WinFsp creates a missing directory and removes it again when the filesystem goes away.
+WinFsp creates the directory itself and removes it again when the filesystem goes away, so the path must be free. An existing directory is refused with "mount point in use" even when it is empty.
 
 Prefer `127.0.0.1` over `localhost`. Windows resolves `localhost` to `::1` first, and a filer listening only on IPv4 will refuse the connection.
 
@@ -71,7 +71,7 @@ Entries whose names Windows cannot represent are invisible from a Windows mount,
 
 ### Troubleshooting
 
-**"WinFsp refused to mount S:"** — WinFsp is not installed, the drive letter is taken, or the directory being mounted over is not empty. `net use` lists the drive letters in use.
+**"WinFsp refused to mount S:"** — WinFsp is not installed, the drive letter is taken, or the directory path already exists. `net use` lists the drive letters in use.
 
 **The mount exits reporting it cannot reach the filer** — check the filer's gRPC port, which is its HTTP port plus 10000 (`8888` → `18888`). It is the gRPC port the mount dials, so a filer answering on HTTP is not proof it is reachable. Use `127.0.0.1` rather than `localhost`.