Clarifies wording of source form for index frequency (#47)

lib/pinchflat_web/controllers/sources/source_html/source_form.html.heex

@@ -24,7 +24,7 @@
     options={friendly_index_frequencies()}
     type="select"
     label="Index Frequency"
-    help="Time between one index of this source finishing and the next one starting. Setting to 'Never' will still run an initial index but no subsequent ones"
+    help="Time between one index of this source finishing and the next one starting. Setting to 'On Create' will still run an initial index but no subsequent ones"
   />
 
   <.input