docs: put uvx retrobios in the macOS, Linux tabs

scripts/generate_site.py

@@ -11951,6 +11951,11 @@ def generate_which_pack() -> str:
     # handheld recording (sitesteps).
     box_tabs = (*all_tabs, "device")
     box_steps, box_demos = sitesteps.install_box(box_tabs)
+    # Python is on most Linux and macOS machines: the package runs the same
+    # installer there without the bootstrap.
+    for tab in ("macos", "linux"):
+        box_demos[tab] = [*box_demos[tab],
+                          f"With Python 3.8 or newer, `{PACKAGE_COMMAND}` does the same.", ""]
     lines = [
         "---",
         f"terms: {', '.join(IOS_TERMS)}",
@@ -12001,8 +12006,6 @@ def generate_which_pack() -> str:
         "On Batocera, Recalbox and other game systems, run it on the device. "
         "The setup's page shows how.",
         "",
-        f"With Python, `{PACKAGE_COMMAND}` does the same.",
-        "",
         *first_screen_words(),
         "",
         *trust_box(""),