updated Readme.scons.txt file

updated Readme.scons.txt file

the build script for each platform is not updated.
so I updated the build script and options.

Change-Id: I5e4298b77fae1bfdacd7539fb199d82afdc7a550
Signed-off-by: hyuna0213.jo <hyuna0213.jo@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/4393
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Naga Ashok Jampani <jn.ashok@samsung.com>
Reviewed-by: Jaehong Jo <jaehong.jo@samsung.com>
Reviewed-by: Jon A. Cruz <jonc@osg.samsung.com>
(cherry picked from commit 0329bfc2565693c376fdc6e71d16685f11231619)
Reviewed-on: https://gerrit.iotivity.org/gerrit/4539