Don't upload elements/README.md.
Don't upload elements/README.md.

I noticed that when deploying, appcfg.py complains about not knowing the mimetype of README.md while uploading. This is a minor tweak to app.yaml to make it stop uploading that file.

Review URL: https://codereview.chromium.org/1463703003

sahiljain/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,benschmaus/catapult,catapult-project/catapult,catapult-project/catapult,SummerLW/Perf-Insight-Report,catapult-project/catapult,sahiljain/catapult,catapult-project/catapult-csm,SummerLW/Perf-Insight-Report,benschmaus/catapult,catapult-project/catapult,benschmaus/catapult,SummerLW/Perf-Insight-Report,benschmaus/catapult,benschmaus/catapult,catapult-project/catapult-csm,benschmaus/catapult,catapult-project/catapult,sahiljain/catapult,SummerLW/Perf-Insight-Report,sahiljain/catapult,sahiljain/catapult,sahiljain/catapult,SummerLW/Perf-Insight-Report,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult,catapult-project/catapult,SummerLW/Perf-Insight-Report,benschmaus/catapult,catapult-project/catapult-csm