README: recommend Debian for BR2

info about sdk

README.md

@@ -3,12 +3,16 @@ Opensource development package for Miyoo handhelds
 
 ## Install
 
+It is assumed you're using Debian based distro, others like Arch or Fedora may brake at build time.
+
 ### Install necessary packages
+
 ``` shell
 sudo apt install -y wget unzip build-essential git bc swig libncurses-dev libpython3-dev libssl-dev cpio rsync subversion python3 mercurial imagemagick btrfs-progs
 ```
 
 ### Download BSP
+
 ```shell
 git clone https://github.com/MiyooCFW/buildroot
 ```
@@ -30,13 +34,23 @@ make miyoo_musl_defconfig
 ```
 
 ### Regular build
+
+- image
+
 ```shell
 make
 ```
 
+- image & sdk
+
+```shell
+make sdk
+```
+
 ## Speed up build progress
 
 ### Compile speed
+
 If you have a multicore CPU, you can try
 ```
 make -j ${YOUR_CPU_COUNT}
@@ -48,6 +62,7 @@ or buy a powerful PC for yourself.
 load output/images/miyoo-cfw-*.img on sdcard
 
 ## First booting device
+
 You will have to answer a few questions on first boot, represented on graphic below:
 ![flashing procedure](firstboot_procedure.drawio.png)