Add some summon-arm-toolchain hints.

README

@@ -15,7 +15,6 @@ programming manuals, and application notes. The code is meant to be used
 with a GCC toolchain for ARM (arm-elf or arm-none-eabi), flashing of the
 code to a microcontroller can be done using the OpenOCD ARM JTAG software.
 
-
 Status and API
 --------------
 
@@ -80,6 +79,11 @@ elsewhere, use the following syntax:
 
  $ DESTDIR=/opt make install
 
+The recommended location is to install into your toolchain directory, e.g.
+/home/someuser/sat for a toolchain built using the summon-arm-toolchain
+script from https://github.com/esden/summon-arm-toolchain.
+
+ $ DESTDIR=~/sat make install
 
 Coding style and development guidelines
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