Added instruction to install dos2unix before Arduino build in readme doc.
Added instruction to install dos2unix before Arduino build in readme doc.

This commit also includes explanation of the newer "SHIELD" option
for Arduino builds (ie. the current Arduino Shield on your Arduino
device).
 
Change-Id: I4b86fef5af77e567b19fcbab19cf87b23b5d576a
Signed-off-by: Joseph Morrow <74b1946a3796b7d1c8ad79fee44616e505fb0cee@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1765
Tested-by: jenkins-iotivity <09cb29e8a2b473a2c978382eec13ee06fa017bda@opendaylight.org>
Reviewed-by: Erich Keane <ec9f61fe526c14bb62c55d7c978f025ee6b3583d@intel.com>

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