[ssci] Uplift third_party/private_membership metadata

This CL:
* updates the URL in the README.chromium file in
/third_party/private_membership to be a bit more descriptive; and
* uses the "Date" field instead of "Version" for versioning info.

This CL was uploaded by git cl split.

R=sergiyb@chromium.org

Bug: b:290296624
Change-Id: I0a36b706cae2dbf7434d5a8bc234b221cf5478fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4945232
Auto-Submit: Anne Redulla <aredulla@google.com>
Commit-Queue: Sergiy Belozorov <sergiyb@chromium.org>
Reviewed-by: Sergiy Belozorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1215364}
NOKEYCHECK=True
GitOrigin-RevId: fd101faf10e368665b35f1b31760515b4e19f8b9
1 file changed