Updated README for makefile support

README.md

@@ -5,7 +5,7 @@ This repository depend on the  [tinyusb](https://github.com/hathach/tinyusb/tree
 
     git submodule update --init
 
-## Build with makefile
+## Option 1: Build with makefile
 
 Navigate to `src/singlebank` (recommended) or `src/dualbank` (work in progress), and use feather52840 target for building bootloader.
 
@@ -19,7 +19,29 @@ To only flash S140
 
 	make flash_sd
 
-## Build using Segger Embeded Studio
+### Common makefile problems
+
+#### 1. `arm-none-eabi-gcc`: No such file or directory
+
+If you get the following error:
+
+```
+$ make feather52840
+Compiling file: dfu_single_bank.c
+/bin/sh: /usr/bin/arm-none-eabi-gcc: No such file or directory
+make: *** [_build/dfu_single_bank.o] Error 127
+```
+
+You make need to edit the `Makefile` (for example `src/singlebank/Makefile`),
+and update the `GNU_INSTALL_ROOT` to point to the root path of your GCC ARM
+toolchain.
+
+#### 2. `mergehex: No such file or directory`
+
+Make sure that `mergehex` is available from the command-line. This binary is
+part of of Nordic's [nRF5x Command Line Tools](http://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.tools%2Fdita%2Ftools%2Fnrf5x_command_line_tools%2Fnrf5x_installation.html).
+
+
+## Option 2: Build using Segger Embeded Studio
 
 For better debugging you can also use SES, The project file is located at `src/segger/nrf52840_bootloader.emProject`.  Note: the SES only flash the bootloader when you click download, you need to flash Softdevice beforehand if you haven't done so ( use `make flash_sd` mentioned above )
-