doc: added RTD badge to README

Signed-off-by: Paul Horton <[email protected]>

Author: madpah

README.md

@@ -3,7 +3,8 @@
 [![shield_gh-workflow-test]][link_gh-workflow-test]
 [![shield_pypi-version]][link_pypi]
 [![shield_conda-forge-version]][link_conda-forge]
-[![shield_license]][license_file]  
+[![shiled_rtd]][link_rtd]
+[![shield_license]][license_file]
 [![shield_website]][link_website]
 [![shield_slack]][link_slack]
 [![shield_groups]][link_discussion]
@@ -55,6 +56,7 @@ See the [LICENSE][license_file] file for the full license.
 [shield_gh-workflow-test]: https://img.shields.io/github/workflow/status/CycloneDX/cyclonedx-python-lib/Python%20CI/main?logo=GitHub&logoColor=white "build"
 [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"
+[shiled_rtd]: https://readthedocs.org/projects/cyclonedx-python-library/badge/?version=latest "Read the Docs"
 [shield_license]: https://img.shields.io/github/license/CycloneDX/cyclonedx-python-lib "license"
 [shield_website]: https://img.shields.io/badge/https://-cyclonedx.org-blue.svg "homepage"
 [shield_slack]: https://img.shields.io/badge/slack-join-blue?logo=Slack&logoColor=white "slack join"
@@ -63,6 +65,7 @@ See the [LICENSE][license_file] file for the full license.
 [link_gh-workflow-test]: https://github.com/CycloneDX/cyclonedx-python-lib/actions/workflows/poetry.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_rtd]: https://cyclonedx-python-library.readthedocs.io/en/latest/?badge=latest
 [link_website]: https://cyclonedx.org/
 [link_slack]: https://cyclonedx.org/slack/invite
 [link_discussion]: https://groups.io/g/CycloneDX