Add Otel demo link to Getting Started Dev (#6683)

Author: B-Mahdj

content/en/docs/getting-started/dev.md

@@ -22,6 +22,9 @@ natively:
 
 - [How can I add native instrumentation to my library?](../../concepts/instrumentation/libraries/)
 
+If you are looking for a set of applications to try things out, you will find
+our official [OpenTelemetry demo](/ecosystem/demo/) useful.
+
 Next, you can deep dive into the documentations for the
 [language](../../languages/) you are using: