[chore] Add OpenSSF Scorecard badge to README

[thompson-tomo]

Changes

Adds the openssf scorecard to the project readme. The best practise should be done by a maintainer as it requires registering project which can be done via https://www.bestpractices.dev/en/projects/new

[!IMPORTANT] Pull requests acceptance are subject to the triage process as described in Issue and PR Triage Management. PRs that do not follow the guidance above, may be automatically rejected and closed.

Merge requirement checklist

• [x] CONTRIBUTING.md guidelines followed.
• [ ] Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• [ ] Links to the prototypes or existing instrumentations (when adding or changing conventions)