feat: adjust documentation for builds with SoftDevice S340

Author: JuergenLeber

lib/softdevice/s340_nrf52_7.0.1/readme.md

@@ -5,12 +5,17 @@ The SoftDevice S340 is closed-source, not publicly available and is only distrib
 In order to be able to download the required ANT+ capable SoftDevice and place SoftDevice S340 v7.0.1 files here. You need to register an 'ANT+ Adopter' account at [thisisant.com](https://www.thisisant.com/register/). After around one business day you will receive access to the resources there. Then do the following steps:
 - Download the SoftDevice S340 v7.0.1 [(here)](https://www.thisisant.com/developer/components/nrf52832#tab_protocol_stacks_tab) and extract its contents
 - Under `lib/softdevice` in this repository there is a folder called `s340_nrf52_7.0.1`
-    - Copy the API folder `ANT_s340_nrf52_7.0.1.API`, the license agreement `License_Agreement_ANT_Softdevice_rev3_3.pdf` and the hex file `ANT_s340_nrf52_7.0.1.hex` from the extracted contents to it.
+    - Copy the API folder `ANT_s340_nrf52_7.0.1.API`, the license agreement `License_Agreement_ANT_Softdevice_rev3_3.pdf` and the hex file `ANT_s340_nrf52_7.0.1.hex` from the extracted contents to it
     - Rename the API folder to `s340_nrf52_7.0.1_API`
     - Rename the hex file to `s340_nrf52_7.0.1_softdevice.hex`
-    - Modify `lib/softdevice/s340_nrf52_7.0.1_API/include/nrf_sdm.h` on line 191 and remove the two slashes at the beginning of `//#define...` to use the *evaluation key* for the ANT SoftDevice.
+    - Check `lib/softdevice/s340_nrf52_7.0.1_API/include/nrf_sdm.h` on line 191 to get an *evaluation key* for the ANT SoftDevice which can later be used for the `ANT_LICENSE_KEY` parameter
     - **VERY IMPORTANT:** You MUST obtain a valid commercial license key BEFORE releasing a product to market that uses the ANT SoftDevice!
 
+To use the SoftDevice S340 with an existing board the `SD_NAME`, `SD_VERSION` and `ANT_LICENSE_KEY` parameters can just be passed to the command line of the `make` command, e.g.:  
+```
+make BOARD=xiao_nrf52840_ble_sense SD_NAME=s340 SD_VERSION=7.0.1 ANT_LICENSE_KEY=<YOUR_LICENSE_KEY_OR_EVALUATION_KEY> all
+```
+
 To add or modify a board with an ANT+ capable SoftDevice S340 the `SD_VERSION` and `SD_NAME` parameters in the corresponding `board.mk` file have to be set:
 ```
 SD_VERSION = 7.0.1