doc: Add more comments in bootloader example

Author: fanghuaqi

example/baremetal/bootloader/main.c

@@ -137,9 +137,14 @@
  *  ![ScreenShot of bootloader under baremetal](pic/images/example/emsk/emsk_bootloader.jpg)
  *
  * ### Extra Comments
- *     Bootrom of EMSK1.x is not able to load secondary bootloader on SPIFlash,
- *     you need a modified EMSK1.x mcs file to enable this function,
- *     please send request in forum about this mcs file.
+ *     - Bootrom of EMSK1.x is not able to load secondary bootloader on SPIFlash, you need a modified EMSK1.x mcs file to enable this function, please send request in forum about this mcs file.
+ *     - Make sure that the bootloader can only load application for extract the same core you built for.
+ *     - Bootloader example only support arc core configuration which has DDR with cache enabled.
+ *     - Bootloader example runs in DDR ram, not in CCM.
+ *     - Bootloader example itself can be treated as a ntshell example, you can run some ntshell commands using this example.
+ *     - Supported core configurations
+ *       + EMSK 1.1: EM6, EM6GP
+ *       + EMSK 2.2/2.3: EM7D, EM11D
  */
 
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