docs: captouch: Add a note that petal 5 is partially broken in the driver

See https://git.flow3r.garden/flow3r/flow3r-firmware/-/blob/main/components/flow3r_bsp/flow3r_bsp_captouch.c#L125-159

docs/api/captouch.rst

 ``captouch`` module
 ===================
 
+.. note::
+
+   Because of a driver quirk, the top pad of the petal 5 is currently not working,
+   resulting in that petal only reporting half of its supposed range.
+
 .. automodule:: captouch
    :members:
    :undoc-members: