Add redbubble link to Airflow merch (apache#10359)

* Add redbubble link to Airflow merch

* Update README.md

Co-authored-by: Kamil Breguła <mik-laj@users.noreply.github.com>

Co-authored-by: Kamil Breguła <mik-laj@users.noreply.github.com>

README.md

@@ -54,6 +54,7 @@ Use Airflow to author workflows as directed acyclic graphs (DAGs) of tasks. The
 - [Who uses Apache Airflow?](#who-uses-apache-airflow)
 - [Who Maintains Apache Airflow?](#who-maintains-apache-airflow)
 - [Can I use the Apache Airflow logo in my presentation?](#can-i-use-the-apache-airflow-logo-in-my-presentation)
+- [Airflow merchandise](#airflow-merchandise)
 - [Links](#links)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
@@ -653,6 +654,11 @@ If you would like to become a maintainer, please review the Apache Airflow
 
 Yes! Be sure to abide by the Apache Foundation [trademark policies](https://www.apache.org/foundation/marks/#books) and the Apache Airflow [Brandbook](https://cwiki.apache.org/confluence/display/AIRFLOW/Brandbook). The most up to date logos are found in [this repo](/docs/img/logos) and on the Apache Software Foundation [website](https://www.apache.org/logos/about.html).
 
+## Airflow merchandise
+
+If you would love to have Apache Airflow stickers, t-shirt etc. then check out
+[Redbubble Shop](https://www.redbubble.com/i/sticker/Apache-Airflow-by-comdev/40497530.EJUG5).
+
 ## Links
 
 - [Documentation](https://airflow.apache.org/docs/stable/)