Cleanup README

README.md

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+# Matplotlib Sphinx Theme
+
+This is the official Sphinx theme for Matplotlib documentation. It extends the
+`pydata-sphinx-theme` project, but adds custom styling and a navigation bar.
+
+A demo of the theme built with the `main` branch can be seen at
+https://matplotlib.org/mpl-sphinx-theme/.
+
+When creating a Matplotlib subproject you can include this theme by changing this
+line in your `conf.py` file
+
+```python
+html_theme = 'mpl_sphinx_theme'
+```
+
+And by including `mpl_sphinx_theme` as a requirement in your documentation
+installation.
+
+See the `docs/conf.py` file for other settings.
+
+There are two main templates that replace the defaults in `pydata-sphinx-theme`:
+
+```
+navbar_center = mpl_nav_bar.html
+navbar_end = mpl_icon_links.html
+```
+
+Note that the logo options need not be specified as they are included in theme
+initialization. The logo is stored at
+`mpl_sphinx_theme/static/logo_{light,dark}.svg`.
+
+To change the top navbar, edit `mpl_sphinx_theme/mpl_nav_bar.html`
+
+To change the social icons, edit `mpl_sphinx_theme/mpl_icon_links.html`
+
+To change the style, edit `mpl_sphinx_theme/static/css/style.css`
+
+## Overriding hard coded elements
+
+This theme is primarily designed to be used with subprojects that are part of the main
+Matplotlib webiste (e.g., [our cheatseets](https://github.com/matplotlib/cheatsheets)
+and [list of third-party packages](https://github.com/matplotlib/mpl-third-party)).
+As such several elements are hard coded. However, the theme may also be used by
+other subprojects that need to change the hard-coded defaults.
+The following sections explain how to reset these back to their defaults by modifying
+`html_theme_options` in `conf.py`.
+
+### Header section links
+
+Use a copy of [the default pydata-sphinx-theme navbar](https://github.com/pydata/pydata-sphinx-theme/blob/main/src/pydata_sphinx_theme/theme/pydata_sphinx_theme/components/navbar-nav.html) and set the `'navbar_center'` key to this HTML file in `html_theme_options`.
+
+## Building
+
+To build the theme with a sample page, navigate into the `doc/` directory and run
+
+```
+make html
+```
+
+The built html pages can be found in `doc/_build/html/`
+
+## Releasing
+
+This project [uses GitHub Actions](https://github.com/matplotlib/mpl-sphinx-theme/blob/main/.github/workflows/release.yml)
+to automatically push a new release to PyPI whenever a release is made.
+
+For example, to release a new `3.9.0` version of `mpl-sphinx-theme`:
+
+- be sure to edit `mpl_sphinx_theme/_version.py`
+- checkout the commit you would like to release
+- add a git tag
+- push the tag to the `matplotlib/mpl-sphinx-theme` repository
+
+```sh
+git checkout <commit-hash>
+git tag -s -a v3.9.0 -m 'REL: 3.9.0'
+git push upstream --tags
+```
+
+Finally, [turn the tag into a GitHub release](https://github.com/matplotlib/mpl-sphinx-theme/releases/new).
+
+Update the required `mpl-sphinx-theme` version in the following files:
+
+- [matplotlib/matplotlib](https://github.com/matplotlib/matplotlib): requirements/doc/doc-requirements.txt
+- [matplotlib/mpl-brochure-site](https://github.com/matplotlib/mpl-brochure-site): requirements.txt
+- [matplotlib/mpl-third-party](https://github.com/matplotlib/mpl-third-party): docs/requirements.txt
+- [matplotlib/governance](https://github.com/matplotlib/governance): requirements-doc.txt
+- [matplotlib/mpl-gui](https://github.com/matplotlib/mpl-gui): requirements-doc.txt