Update SUMMARY.md

Hopefully I'm adding the new exit output to the summary file to the PR where the exit docs are being added.


Signed-off-by: Lynette  Miles <[email protected]>

Author: esmerel

SUMMARY.md

@@ -162,6 +162,7 @@
   * [Counter](pipeline/outputs/counter.md)
   * [Datadog](pipeline/outputs/datadog.md)
   * [Elasticsearch](pipeline/outputs/elasticsearch.md)
+  * [Exit](pipeline/outputs/exit.md)
   * [File](pipeline/outputs/file.md)
   * [FlowCounter](pipeline/outputs/flowcounter.md)
   * [Forward](pipeline/outputs/forward.md)