Readme: Add Nextflow logo, add link to community forum

Author: ewels

README.md

@@ -4,6 +4,15 @@
 
 [![Open in GitHub Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/nextflow-io/training?quickstart=1&ref=master)
 
+<p align="center">
+  <a href="https://nextflow.io/">
+    <picture>
+        <source media="(prefers-color-scheme: dark)" width="350" srcset="https://github.com/seqeralabs/logos/blob/master/nextflow/nextflow_logo_color_darkbg.png?raw=true">
+        <img alt="Nextflow Logo" width="350" src="https://github.com/seqeralabs/logos/blob/master/nextflow/nextflowc_logo_color.png?raw=true">
+    </picture>
+  </a>
+</p>
+
 Welcome to the Nextflow training repository!
 We are excited to have you on the path to writing reproducible and scalable scientific workflows using Nextflow.
 
@@ -13,6 +22,8 @@ We are excited to have you on the path to writing reproducible and scalable scie
 
 - 📚 Nextflow documentation: <https://www.nextflow.io/docs/latest/>
 
+- 💬 Community forum: <https://community.seqera.io/nextflow>
+
 ## Contributions
 
 We welcome fixes and improvements from the community. Please fork the repository and create pull-requests with any improvements you'd like to suggest to the docs.