git: openjdk/jdk-sandbox: classfile-api-dev-branch: added JCov report link to README.md

[Adam Sotona]

Changeset: 51faeee7
Author:    Adam Sotona <asotona at openjdk.org>
Date:      2022-08-31 16:30:49 +0000
URL:       https://git.openjdk.org/jdk-sandbox/commit/51faeee746368517c576ec037007fcf91cc86511

added JCov report link to README.md

! README.md