Add README for IoTivity-Constrained
Add README for IoTivity-Constrained

This will be a living document. It currently provides an
introductory overview of the project, architecture and build
instructions for existing samples.

Change-Id: I6cd2fb8215b9271757c4412a13b267eaeed6116d
Signed-off-by: Kishen Maloor <c62ddea3cd661a9268bff15f07fc2229cdc9ac02@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/10985
Reviewed-by: Thiago Macieira <0ed1648d92ca0373297a182b1dba1b974ad10d88@intel.com>
Tested-by: Thiago Macieira <0ed1648d92ca0373297a182b1dba1b974ad10d88@intel.com>

iotivity/iotivity-constrained,iotivity/iotivity-constrained,iotivity/iotivity-constrained,iotivity/iotivity-constrained