Add link to the Discord community server (#13)

Author: Ostrzyciel

docs/documentation/contribute.md

@@ -6,6 +6,10 @@
 
 RiverBench is an open, [community-driven](maintainers.md) project, so you are more than welcome to contribute. This page explains how to do it.
 
+## Chat with the community
+
+If you have any questions or want to discuss your ideas, feel free to join our **[Discord chat](https://discord.gg/HYkutTWsJ9)**.
+
 ## Reporting benchmark results
 
 If you have run a benchmark using RiverBench's datasets or tasks, **we highly encourage you to [share your results](reporting-results.md)**. After filling out a simple form, your benchmark run will be [listed on the RiverBench website](../results/index.md) (along with proper citation, of course) in a machine- and human-readable format. See our dedicated brief guide on **[reporting benchmark results](reporting-results.md)** for more details.