update documentation to use markdown (part 2)

Adding `CONTRIBUTING.md`, missed from a previous commit [1].

[1]: 4e680b4

Signed-off-by: James Knight <[email protected]>

CONTRIBUTING.md

@@ -0,0 +1,93 @@
+# Contributing
+
+Contributions to this extension are welcome and much appreciated.
+
+## Reporting issues
+
+Bugs, enhancements and more can be reported to this extension's GitHub
+[issue tracker][issues]. It is recommended to search for a related issue
+before attempting to submit a new issue.
+
+When reporting a bug, it is recommended to include at least the following:
+
+- sphinxcontrib-confluencebuilder's extension version
+- Python version
+- Sphinx version
+
+A more detailed report can be generated and included in the bug using the
+following command from inside a Sphinx project:
+
+```shell
+sphinx-build-confluence report
+ (or)
+python -m sphinxcontrib.confluencebuilder report
+```
+
+Additional logs from a `sphinx-build` attempt can be helpful as well (if
+applicable).
+
+## Submitting changes
+
+Contributions can be provided as [pull requests][prs] to this extension's
+GitHub project. New contributors should familiarize themselves with the
+following:
+
+- **(required)** Sign your work ([Developer’s Certificate of Origin][dcod]).
+  This is confirmed with the inclusion of `Signed-off-by` in submitted
+  commit messages.
+- Builds are required\* to pass to be accepted (\* with some exceptions
+  in very specific scenarios). When a pull request is submitted, continuous
+  integration tests will be invoked. A developer can invoke `tox` at the
+  root of the checked out repository to validate changes before submitting
+  a pull request.
+- Keep a narrow scope for proposed changes. Submitting multiple feature
+  changes in a single pull request is not always helpful. Use multiple
+  commits to separate changes over stacking all changes in a single commit
+  (for example, related implementation and documentation changes can be
+  submitted in a single pull request, but are best presented in their own
+  individual commits).
+- Add unit tests (if applicable). Adding unit tests to validate new changes
+  helps build confidence for the new modifications and helps prevent future
+  changes from breaking the new feature/fix.
+- Update documentation (if applicable). If a new change introduces, for
+  example, a new configuration entry or markup support has changed with
+  a request, do not forget to update respective documentation as well.
+- **Do not** update `AUTHORS` or `CHANGES.rst`. Author information and
+  change log information are managed by this extension's maintainers. These
+  files may be updated during a development window and will always be updated
+  during a release. If a contributor does not wish to add themselves to the
+  `AUTHORS` document, they may opt-out be explicitly indicating in a pull
+  request or issue. In select cases, users may open pull requests for these
+  documents if corrections are needed.
+
+While maintainers will help strive to review, merge changes and provide
+support (when possible), the process may take some time. Please be patient
+and happy coding.
+
+## Guidelines
+
+This extension will support various Python interpreter versions, Sphinx
+versions and Confluence versions. The goal of this extension is to include
+support for all stable Python interpreters and Confluence versions which
+have yet to be marked as end-of-life as well as support Sphinx versions
+with a suggested maximum of five major-minor trees.
+
+- Python interpreters that have not been marked as [end-of-life][python-eol]
+  will be supported by this extension.
+- Supported Confluence versions will be supported versions listed in
+  [Atlassian Support End of Life Policy][confluence-eol].
+- Supported Sphinx versions include the last five major-minor versions
+  of the application (e.g. 3.2.x, 3.1.x, 3.0.x, 2.4.x, 2.3.x).
+
+[PEP 8][pep8] is a standard styling guide for Python projects and is
+recommended for consideration when making contributions. Default linters
+configured in tox are required to pass. Note that select exceptions may
+be used.
+
+
+[confluence-eol]: https://confluence.atlassian.com/support/atlassian-support-end-of-life-policy-201851003.html
+[dcod]: https://developercertificate.org/
+[issues]: https://github.com/sphinx-contrib/confluencebuilder/issues
+[pep8]: https://peps.python.org/pep-0008/
+[prs]: https://github.com/sphinx-contrib/confluencebuilder/pulls
+[python-eol]: https://devguide.python.org/versions/