Workers: Add Design Docs for ES modules to core/workers/README.md

This CL adds design docs for ES modules for dedicated/shared workers.

Bug: n/a
Change-Id: I93b1ec931a05ffadb139ca37438a0d95b92ccb53
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2061917
Commit-Queue: Eriko Kurimoto <elkurin@google.com>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#742516}

third_party/blink/renderer/core/workers/README.md

@@ -178,6 +178,8 @@ in the following files and directories to avoid breakage.
 
 # References
 
+- [ES Modules for Shared Workers](https://docs.google.com/document/d/1sSdYdSOLd5zvnNGeVNlBqfTZs_VRPIrrigV3SlMnWjg/edit?usp=sharing) (Feb 19, 2020)
 - [WorkerGlobalScope Initialization](https://docs.google.com/document/d/1JCv8TD2nPLNC2iRCp_D1OM4I3uTS0HoEobuTymaMqgw/edit?usp=sharing) (April 1, 2019)
 - [Worker / Worklet Internals](https://docs.google.com/presentation/d/1GZJ3VnLIO_Pw0jr9nRw6_-trg68ol-AkliMxJ6jo6Bo/edit?usp=sharing) (April 19, 2018)
+- [ES Modules for Dedicated Workers](https://docs.google.com/document/d/1IMGWAK7Wq37mLehwkbysNRBBnhQBo3z2MbYyMkViEnY/edit?usp=sharing) (Mar 8, 2018)
 - [Design of UseCounter for workers](https://docs.google.com/document/d/1VyYZnhjBdk-MzCRAcX37TM5-yjwTY40U_J9rWnEAo8c/edit?usp=sharing) (Feb 14, 2017)