README.md: add steps for updating intel-arduino-tools

Author: eriknyquist

README.md

@@ -21,6 +21,10 @@ If you wish to use the latest **untested** changes, follow these instructions.
 6. Delete the content of the directory from step 5, and replace it with the
    content of the "corelibs-arduino101-master" folder in the zip from step 2.
 
+Note: your [tools](https://github.com/01org/intel-arduino-tools), found in
+`Arduino15/packages/Intel/tools/arduino101load/<version>/`, may also need to
+be updated to the latest snapshot.
+
 Future upgrades may fail since the internal contents were modified by hand. In
 order to recover, shut down the IDE, delete the entire `Arduino15` directory,
 then restart the IDE.