[docs] custom script examples, [build] move CMS make to app via event_handlers.on_build

docs/dev/custom_script_examples/docs.dev.custom_script.read_only.md

@@ -0,0 +1,13 @@
+---
+{
+	"_label": "Make an Item read-only after Saving"
+}
+---
+Use the method `cur_frm.set_df_property` to update the field's display.
+
+In this script we also use the `__islocal` property of the doc to check if the document has been saved atleast once or is never saved. If `__islocal` is `1`, then the document has never been saved.
+
+	cur_frm.cscript.custom_refresh = function(doc) {
+	    // use the __islocal value of doc, to check if the doc is saved or not
+	    cur_frm.set_df_property("myfield", "read_only", doc.__islocal ? 0 : 1);
+	}