[next_stage] Help text for next_stage module (#7923)

    Resolves  #7871

Author: AlexandraLivadas

modules/next_stage/help/next_stage.md

@@ -0,0 +1,5 @@
+# Next Stage
+
+This module prompts for the date of the current visit to start the Visit Stage of the session and populate the instrument list page with the relevant instruments. 
+
+Once the date of the visit is entered and the user clicks on "Start Visit", the user will be redirected to a page with a success message and a link to the updated instrument list page.