doc/user: rename filenames with underscores to dashes

Everything else is, let's be consistent here.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

doc/user/features.rst

@@ -13,7 +13,7 @@ to be useful.
 .. toctree::
    :maxdepth: 1
 
-   button_debouncing.rst
+   button-debouncing.rst
    clickpad-softbuttons.rst
    gestures.rst
    middle-button-emulation.rst

doc/user/meson.build

@@ -68,7 +68,7 @@ src_rst = files(
 	'absolute-coordinate-ranges.rst',
 	'architecture.rst',
 	'building.rst',
-	'button_debouncing.rst',
+	'button-debouncing.rst',
 	'clickpad-softbuttons.rst',
 	'contributing.rst',
 	'device-configuration-via-udev.rst',