refactor(docs): move from reST to Markdown (#157)

Convert docs from reStructuredText to Markdown so that the changelog
file is compatible with Release Please.

AUTHORS.md

@@ -0,0 +1,9 @@
+# Authors
+
+The list of contributors in alphabetical order:
+
+- [Audrius Mecionis](https://orcid.org/0000-0002-3759-1663)
+- [Bruno Rosendo](https://orcid.org/0000-0002-0923-3148)
+- [Giuseppe Steduto](https://orcid.org/0009-0002-1258-8553)
+- [Marco Donadoni](https://orcid.org/0000-0003-2922-5505)
+- [Tibor Simko](https://orcid.org/0000-0001-7202-5803)

CONTRIBUTING.rst → CONTRIBUTING.md

@@ -1,20 +1,18 @@
-Contributing
-============
+# Contributing
 
 Bug reports, issues, feature requests, and other contributions are welcome. If you find
 a demonstrable problem that is caused by the REANA code, please:
 
-1. Search for `already reported problems
-   <https://github.com/reanahub/reana-client-go/issues>`_.
+1. Search for [already reported problems](https://github.com/reanahub/reana-client-go/issues).
 2. Check if the issue has been fixed or is still reproducible on the
    latest `master` branch.
 3. Create an issue, ideally with **a test case**.
 
 If you create a pull request fixing a bug or implementing a feature, you can run
 the tests to ensure that everything is operating correctly:
 
-.. code-block:: console
-
-    $ make test
+```console
+$ make test
+```
 
 Each pull request should preserve or increase code coverage.

README.md

@@ -0,0 +1,30 @@
+# REANA-Client-Go
+
+[![image](https://github.com/reanahub/reana-client-go/workflows/CI/badge.svg)](https://github.com/reanahub/reana-client-go/actions)
+[![image](https://codecov.io/gh/reanahub/reana-client-go/branch/master/graph/badge.svg)](https://codecov.io/gh/reanahub/reana-client-go)
+[![image](https://img.shields.io/badge/discourse-forum-blue.svg)](https://forum.reana.io)
+[![image](https://img.shields.io/github/license/reanahub/reana.svg)](https://github.com/reanahub/reana-client-go/blob/master/LICENSE)
+
+# About
+
+REANA-Client-Go is a component of the [REANA](https://www.reana.io/) reusable and
+reproducible research data analysis platform. It provides a command-line tool that allows
+researchers to submit, run, and manage their computational workflows.
+
+- seed workspace with input code and data
+- run computational workflows on remote compute clouds
+- list submitted workflows and enquire about their statuses
+- download results of finished workflows
+
+# Usage
+
+The detailed information on how to install and use REANA can be found in
+[docs.reana.io](https://docs.reana.io).
+
+# Useful links
+
+- [REANA project home page](http://www.reana.io/)
+- [REANA user documentation](https://docs.reana.io)
+- [REANA user support forum](https://forum.reana.io)
+- [REANA-Client-Go known issues](https://github.com/reanahub/reana-client-go/issues)
+- [REANA-Client-Go source code](https://github.com/reanahub/reana-client-go)