docs(next-steps): advertise workflow tutorials and examples (#213)

Closes #143 #171

docs/getting-started/next-steps/index.md

@@ -1 +1,23 @@
 # Next steps
+
+After getting familiarised with REANA, here are possible next steps that you
+can take to get a deeper understanding of the system.
+
+Firstly, you should explore dedicated tutorials for the declarative workflow
+language you would like to use. For example:
+
+- [CWL user guide](https://www.commonwl.org/user_guide/)
+- [Snakemake tutorial](https://snakemake.readthedocs.io/en/stable/tutorial/tutorial.html)
+
+REANA aims at providing a platform for running these workflows seamlessly, so
+getting acquainted with the possibilities of the workflow system is important
+in order to take the full advantage of the paradigm.
+
+Secondly, you may want to explore [several existing REANA analysis
+examples](https://github.com/reanahub?q=demo) on GitHub to see how typical data
+analyses may be containerised and run as automated workflows.
+
+Finally, you can read other dedicated documentation sections on this web site
+for particular topics of interest. For example, if you would like to run
+Jupyter notebooks alongside your workflows, please see [Running
+notebooks](/running-notebooks/) on this web site.