learning_gem5: Update README for Learning gem5

Change-Id: I94485e401bc77207cab68c1e24ef7a6ed83bd43d
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/8946
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>

config: Add configs scripts used in Learning gem5

Added a new directory in configs (learning_gem5) to hold the scripts that are
used in the book. See http://lowepower.com/jason/learning_gem5/ for a working
copy. For now, only the scripts in Part 1: Getting started with gem5
have been added. A separate patch adds tests for these scripts.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>