Add docstring for cron branches (#89)

Albrja/mic-6030/doc-cron-branches

Add docstring for how to handle cron branches in Jenkins
- *Category*: CI
- *JIRA issue*: https://jira.ihme.washington.edu/browse/MIC-6030

Author: albrja

Jenkinsfile

@@ -28,6 +28,11 @@ Note that updating the shared repo will take affect on the next pipeline invocat
 library("vivarium_build_utils@${get_vbu_version()}")
 
 reusable_pipeline(
-    scheduled_branches: ["main", "epic/auto-validation"],
+    scheduled_branches: [
+      // Add additional branches for cron jobs below.
+      // Note: Newly added branches will require a manual trigger of the first build 
+      // for subsequent scheduled builds to run.
+      "main", "epic/auto-validation"
+    ],
     skip_doc_build: true
 )