samples: subsys: display: lvgl: Update README

Update the readme to better describe contents of the sample, which is now
used to showcase the various input device types that LVGL offers.

(cherry picked from commit 9177709)

Original-Signed-off-by: Fabian Blatz <fabianblatz@gmail.com>
GitOrigin-RevId: 9177709
Change-Id: I15401102aa46556731648726c0737ff037189ffd
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5104209
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>
Reviewed-by: Fabio Baltieri <fabiobaltieri@google.com>
Tested-by: Fabio Baltieri <fabiobaltieri@google.com>
Commit-Queue: Fabio Baltieri <fabiobaltieri@google.com>

samples/subsys/display/lvgl/README.rst

@@ -1,17 +1,36 @@
 .. zephyr:code-sample:: lvgl
    :name: LVGL basic sample
-   :relevant-api: display_interface
+   :relevant-api: display_interface input_interface
 
-   Display "Hello World" and a dynamic counter using LVGL.
+   Display a "Hello World" and react to user input using LVGL.
 
 Overview
 ********
 
 This sample application displays "Hello World" in the center of the screen
-and a counter at the bottom which increments every second. If an input driver
-is supported, such as the touch panel controller on mimxrt10{50,60,64}_evk
-boards, "Hello World" is enclosed in a button that changes to the toggled state
-when touched.
+and a counter at the bottom which increments every second.
+Based on the available input devices on the board used to run the sample,
+additional widgets may be displayed and additional interactions enabled:
+
+* Pointer
+      If your board has a touch panel controller
+      (:dtcompatible:`zephyr,lvgl-pointer-input`), a button widget is displayed
+      in the center of the screen. Otherwise a label widget is displayed.
+* Button
+      The button pseudo device (:dtcompatible:`zephyr,lvgl-button-input`) maps
+      a press/release action to a specific coordinate on screen. In the case
+      of this sample, the coordinates are mapped to the center of the screen.
+* Encoder
+      The encoder pseudo device (:dtcompatible:`zephyr,lvgl-encoder-input`)
+      can be used to navigate between widgets and edit their values. If the
+      board contains an encoder, an arc widget is displayed, which can be
+      edited.
+* Keypad
+      The keypad pseudo device (:dtcompatible:`zephyr,lvgl-keypad-input`) can
+      be used for focus shifting and also entering characters inside editable
+      widgets such as text areas. If the board used with this sample has a
+      keypad device, a button matrix is displayed at the bottom of the screen
+      to showcase the focus shifting capabilities.
 
 Requirements
 ************