Rst to myst (scverse#2185)

* rst to markdown

* rst to markdown, configs

* Fix names of files references in dev

* Add myst-parser to doc deps

* Go from ::: to ``` for notes

Didn't really make sense to me for some blocks to use a different syntax.
AFAICT, myst's intent in supporting that was just for a couple markdown editors. IDK.

README.md

@@ -0,0 +1,23 @@
+[![Stars](https://img.shields.io/github/stars/theislab/scanpy?logo=GitHub&color=yellow)](https://github.com/theislab/scanpy/stargazers)
+[![PyPI](https://img.shields.io/pypi/v/scanpy?logo=PyPI)](https://pypi.org/project/scanpy)
+[![PyPIDownloads](https://pepy.tech/badge/scanpy)](https://pepy.tech/project/scanpy)
+[![Conda](https://img.shields.io/conda/dn/conda-forge/scanpy?logo=Anaconda)](https://anaconda.org/conda-forge/scanpy)
+[![Docs](https://readthedocs.com/projects/icb-scanpy/badge/?version=latest)](https://scanpy.readthedocs.io)
+[![Build Status](https://dev.azure.com/theislab/scanpy/_apis/build/status/theislab.scanpy?branchName=master)](https://dev.azure.com/theislab/scanpy/_build)
+
+# Scanpy – Single-Cell Analysis in Python
+
+Scanpy is a scalable toolkit for analyzing single-cell gene expression data
+built jointly with [anndata](https://anndata.readthedocs.io).  It includes
+preprocessing, visualization, clustering, trajectory inference and differential
+expression testing.  The Python-based implementation efficiently deals with
+datasets of more than one million cells.
+
+Discuss usage on the scverse [Discourse]. Read the [documentation].
+If you'd like to contribute by opening an issue or creating a pull request, please take a look at our [contributing guide].
+If Scanpy is useful for your research, consider citing [Genome Biology (2018)].
+
+[contributing guide]: CONTRIBUTING.md
+[discourse]: https://discourse.scverse.org/
+[documentation]: https://scanpy.readthedocs.io
+[genome biology (2018)]: https://doi.org/10.1186/s13059-017-1382-0