demos: remove inconsistent readme

[IAMMX]

Description of the feature or fix

fix #5609
demos: remove inconsistent readme.

Notes

• Update the Documentation if needed.
• Add Examples if relevant.
• Add Tests if applicable.
• If you added new options to lv_conf_template.h run lv_conf_internal_gen.py and update Kconfig.
• Run scripts/code-format.py (astyle needs to be installed) and follow the Code Conventions
• Mark the Pull request as Draft while you are working on the first version, and mark is as Ready when it's ready for review.
• When changes were requested, re-request review to notify the maintainers.
• Help us to review this Pull Request! Anyone can approve or request changes.

[kisvegabor]

Thank you! According to the feedback of the users it's not always clear how to interpret the result of the benchmark. To have some docs about it please add this comment to lv_demo_benchmark() in lv_demo_benchmark.h:

/**
 * Run all benchmark scenes.
 * 
 * On the summary end screen the values shall be interpreted according to the followings:
 * - CPU usage: 
 *    - If `LV_SYSMON_GET_IDLE` is not modified it's measured based on the time spent in
 *      `lv_timer_handler`. 
 *    - If an (RT)OS is used `LV_SYSMON_GET_IDLE` can be changed to a custom function
 *      which returns the idle percentage of idle task.
 * 
 * - FPS: LVGL attempted to render this many times in a second. It's limited based on `LV_DEF_REFR_PERIOD`
 * 
 * - Render time: LVGL spent this much time with rendering only. It's not aware of task yielding,
 *   but simply the time difference between the start and end of the rendering is measured
 * 
 * - Flush time: It's the sum of 
 *     - the time spent in the `fluch_cb` and 
 *     - the time spent with waiting for flush ready.
 */
void lv_demo_benchmark(void);

[IAMMX]

Thank you! According to the feedback of the users it's not always clear how to interpret the result of the benchmark. To have some docs about it please add this comment to lv_demo_benchmark() in lv_demo_benchmark.h

Done.

[kisvegabor]

Thank you!