doc: buildAndProgram: remove node script lv_img_conv mention

Remove node script `lv_img_conv` mention and replace it for
runtime-depency `python3-pil` of python script `lv_img_conv.py`.

doc/buildAndProgram.md

@@ -42,7 +42,7 @@ CMake configures the project according to variables you specify the command line
 **NRF5_SDK_PATH**|path to the NRF52 SDK|`-DNRF5_SDK_PATH=/home/jf/nrf52/Pinetime/sdk`|
 **CMAKE_BUILD_TYPE (\*)**| Build type (Release or Debug). Release is applied by default if this variable is not specified.|`-DCMAKE_BUILD_TYPE=Debug`
 **BUILD_DFU (\*\*)**|Build DFU files while building (needs [adafruit-nrfutil](https://github.com/adafruit/Adafruit_nRF52_nrfutil)).|`-DBUILD_DFU=1`
-**BUILD_RESOURCES (\*\*)**| Generate external resource while building (needs [lv_font_conv](https://github.com/lvgl/lv_font_conv) and [lv_img_conv](https://github.com/lvgl/lv_img_conv). |`-DBUILD_RESOURCES=1`
+**BUILD_RESOURCES (\*\*)**| Generate external resource while building (needs [lv_font_conv](https://github.com/lvgl/lv_font_conv) and `python3-pil` module). |`-DBUILD_RESOURCES=1`
 **TARGET_DEVICE**|Target device, used for hardware configuration. Allowed: `PINETIME, MOY-TFK5, MOY-TIN5, MOY-TON5, MOY-UNK`|`-DTARGET_DEVICE=PINETIME` (Default)
 
 #### (\*) Note about **CMAKE_BUILD_TYPE**