[chore] [receiver/pulsar] docs: add link to Apache Pulsar (#37163)

I didn't know what Pulsar was, this might help other users too.

receiver/pulsarreceiver/README.md

@@ -12,7 +12,7 @@
 [contrib]: https://github.com/open-telemetry/opentelemetry-collector-releases/tree/main/distributions/otelcol-contrib
 <!-- end autogenerated section -->
 
-Pulsar receiver receives logs, metrics, and traces from Pulsar.
+Pulsar receiver receives logs, metrics, and traces from [Apache Pulsar](https://pulsar.apache.org/).
 
 ## Getting Started