fix: offer Lakka's card route from Linux only

Lakka keeps /storage on the card's ext4 partition (Lakka-LibreELEC
4696b48f scripts/mkimage:72, 95), which Windows and macOS do not open, and
its page offered them a card route. card_run is now [linux], and a page
with no Windows route says only Linux opens the card.

scripts/generate_site.py

@@ -4188,7 +4188,11 @@ def _card_route(name: str, display: str, guide: Guide) -> list[str]:
         lead = ("No network here? Run the command on a computer that has one, with a USB "
                 f"drive's folder after `--dest`. Then copy it into {_folder_words(display, extract_to)}.")
         return [lead, "", *terminal_tabs(tabs, args, steps=False)]
-    lead = ("No network? Put the device's card in your computer. After `--dest`, "
+    # A folder on the card's Linux partition: Windows and macOS show the
+    # small boot partition alone, and no folder there fits --dest.
+    put = ("Put the device's card in your computer." if "windows" in tabs
+           else "Only a Linux computer opens the card.")
+    lead = (f"No network? {put} After `--dest`, "
             f"name the folder the device calls `{extract_to}`.")
     return [lead, "", *terminal_tabs(tabs, args, steps=False),
             f"[More on SD cards](../{CARD_ROUTE_FAQ})", ""]