expanded description for "radius" (#4482)

I originally understood the wording around "65535 = pill shaped widget (true circle..." in a way that setting radius to 65535 always gives you a circle, also for widgets that (obviously) have way smaller widths and heights. Working with it a bit I realised it's not that straightforward, and that setting a radius in line with what is set for width/height is the way to go anyway. So I decided to expand the description a bit.

components/lvgl/index.rst

@@ -325,7 +325,7 @@ You can adjust the appearance of widgets by changing their foreground, backgroun
 - **pad_right** (*Optional*, int16): Set the padding on the right, in pixels.
 - **pad_row** (*Optional*, int16): Set the padding between the rows of the children elements, in pixels.
 - **pad_column** (*Optional*, int16): Set the padding between the columns of the children elements, in pixels.
-- **radius** (*Optional*, uint16): The radius to be used to form the widget's rounded corners. 0 = no radius (square corners); 65535 = pill shaped widget (true circle if it has same width and height).
+- **radius** (*Optional*, uint16): The radius to be used to form the widget's rounded corners. 0 = no radius (square corners); 65535 (max) = pill shaped widget (true circle if it has same width and height, radius then should be set to half the width/height).
 - **shadow_color** (*Optional*, :ref:`color <lvgl-color>`): Color used to create a drop shadow under the widget. Defaults to ``0`` (black).
 - **shadow_ofs_x** (*Optional*, int16): Horizontal offset of the shadow, in pixels. Defaults to ``0``.
 - **shadow_ofs_y** (*Optional*, int16): Vertical offset of the shadow, in pixels. Defaults to ``0``.