Documentation: Convert README.rst to README.md rucio#6617

Markdown appears to be more commonly-used (see other Rucio
repositories).  Maybe reStructuredText would have been preferable in a
more complex document, but this one is very simple.

Also apply the convention to have one sentence per line, which will
prove beneficial for future changes.

README.md

@@ -0,0 +1,27 @@
+# Rucio - Scientific Data Management
+
+Rucio is a software framework that provides functionality to organize, manage, and access large volumes of scientific data using customisable policies.
+The data can be spread across globally distributed locations and across heterogeneous data centers, uniting different storage and network technologies as a single federated entity.
+Rucio offers advanced features such as distributed data recovery or adaptive replication, and is highly scalable, modular, and extensible.
+Rucio has been originally developed to meet the requirements of the high-energy physics experiment ATLAS, and is continuously extended to support LHC experiments and other diverse scientific communities.
+
+## Documentation
+
+General information, API/REST description and guides can be found in our [documentation](https://rucio.cern.ch/documentation) or on our [webpage](https://rucio.cern.ch).
+
+## Try it out
+
+We provide a [dockerized environment](https://github.com/rucio/rucio/tree/master/etc/docker/dev) which serves both as a demo environment and a development environment.
+It includes all the necessary preconfigured components for multiple storage and transfers developments.
+
+## Developers
+
+For information on how to contribute to Rucio, please refer and follow our [CONTRIBUTING](https://rucio.cern.ch/documentation/contributing) guidelines. We strongly recommend to use the [dockerized environment](https://github.com/rucio/rucio/tree/master/etc/docker/dev) for development.
+
+## Operators
+
+To learn how to deploy and configure Rucio, consult the [documentation](https://rucio.cern.ch/documentation) available online.
+
+## Getting Support
+
+If you are looking for support, join us on our Slack [support](https://rucio.slack.com/messages/#support) channel, or send an email to our public mailing list [rucio-users@googlegroups.com](mailto:rucio-users@googlegroups.com).