Update glossary.mdx (#502)

added smoketest definition

docs/glossary.mdx

@@ -21,5 +21,6 @@ slug: /glossary
    * [Docs](https://remote-settings.readthedocs.io/en/latest/)
    * [Integration with Experimenter](https://github.com/mozilla/experimenter/tree/main/docs/experimenter#overview)
 * **Rollout**: A single-branch experiment, often the "winning branch" from an experiment, that can be used to "roll out" a feature to your Audience. See the [Rollouts deep dive](/deep-dives/experimenter/rollouts) for more info.
+* **Smoke Test** is a preliminary trial/experiment with minimal setup/limited parameters/minimal user population to ensure that the experiment is operational and that there are no obvious issues. The objective is to catch any major problems early on, allowing us to address them before conducting more in-depth/resource-intensive (stat.sig) experiments.  This is common when there are new pieces (like many newly added telemetry probes or complex targeting or triggers) coming together.  It is better to learn in a small (hundreds instead of hundreds of thousands people) experiment that your message is triggering at the wrong time to the wrong users, or that your telemetry isn't capturing something you need to learn. 
 * **What's the difference between Experimenter and Nimbus** Nimbus is the whole experimentation system (handles enrolling/unenrolling users, sending branch configurations, etc).  Nimbus was the code name of the experimentation project.  If you hear Jetstream, that is the whole analysis system (interfaces with data, runs analysis, formats results).  Experimenter is the customer interface to both Nimbus and Jetstream - that you access at experimenter.services.mozilla.com/.  In Experimenter users can configure experiments, manage them (launch, monitor, end), and can see the results.
 * _More coming soon..._