docs: add OpenSSF Best Practices shield (#532)

Signed-off-by: Jan Kowalleck <jan.kowalleck@gmail.com>

README.md

@@ -5,6 +5,7 @@
 [![shield_rtfd]][link_rtfd]
 [![shield_gh-workflow-test]][link_gh-workflow-test]
 [![shield_coverage]][link_codacy]
+[![shield_ossf-best-practices]][link_ossf-best-practices]
 [![shield_license]][license_file]  
 [![shield_website]][link_website]
 [![shield_slack]][link_slack]
@@ -60,6 +61,7 @@ See the [LICENSE][license_file] file for the full license.
 
 [shield_gh-workflow-test]: https://img.shields.io/github/actions/workflow/status/CycloneDX/cyclonedx-python-lib/python.yml?branch=main&logo=GitHub&logoColor=white "build"
 [shield_coverage]: https://img.shields.io/codacy/coverage/1f9d451e9cdc49ce99c2a1247adab341?logo=Codacy&logoColor=white "test coverage"
+[shield_ossf-best-practices]: https://img.shields.io/cii/level/7956?label=OpenSSF%20best%20practices "OpenSSF best practices"
 [shield_pypi-version]: https://img.shields.io/pypi/v/cyclonedx-python-lib?logo=pypi&logoColor=white&label=PyPI "PyPI"
 [shield_conda-forge-version]: https://img.shields.io/conda/vn/conda-forge/cyclonedx-python-lib?logo=anaconda&logoColor=white&label=conda-forge "conda-forge"
 [shield_rtfd]: https://img.shields.io/readthedocs/cyclonedx-python-library?logo=readthedocs&logoColor=white "Read the Docs"
@@ -68,11 +70,13 @@ See the [LICENSE][license_file] file for the full license.
 [shield_slack]: https://img.shields.io/badge/slack-join-blue?logo=Slack&logoColor=white "slack join"
 [shield_groups]: https://img.shields.io/badge/discussion-groups.io-blue.svg "groups discussion"
 [shield_twitter-follow]: https://img.shields.io/badge/Twitter-follow-blue?logo=Twitter&logoColor=white "twitter follow"
+
 [link_gh-workflow-test]: https://github.com/CycloneDX/cyclonedx-python-lib/actions/workflows/python.yml?query=branch%3Amain
 [link_pypi]: https://pypi.org/project/cyclonedx-python-lib/
 [link_conda-forge]: https://anaconda.org/conda-forge/cyclonedx-python-lib
 [link_rtfd]: https://cyclonedx-python-library.readthedocs.io/en/latest/?badge=latest
 [link_codacy]: https://app.codacy.com/gh/CycloneDX/cyclonedx-python-lib
+[link_ossf-best-practices]: https://www.bestpractices.dev/projects/7956
 [link_website]: https://cyclonedx.org/
 [link_slack]: https://cyclonedx.org/slack/invite
 [link_discussion]: https://groups.io/g/CycloneDX