[formrecognizer] fix readme sample (Azure#15851)

Resolves Azure#15843

Author: kristapratico

sdk/formrecognizer/azure-ai-formrecognizer/README.md

@@ -236,23 +236,25 @@ with open("<path to your form>", "rb") as fd:
     form = fd.read()
 
 poller = form_recognizer_client.begin_recognize_content(form)
-page = poller.result()
-
-table = page[0].tables[0] # page 1, table 1
-print("Table found on page {}:".format(table.page_number))
-print("Table location {}:".format(table.bounding_box))
-for cell in table.cells:
-    print("Cell text: {}".format(cell.text))
-    print("Location: {}".format(cell.bounding_box))
-    print("Confidence score: {}\n".format(cell.confidence))
-
-print("Selection marks found on page {}:".format(page[0].page_number))
-for selection_mark in page[0].selection_marks:
-    print("Selection mark is '{}' within bounding box '{}' and has a confidence of {}".format(
-        selection_mark.state,
-        selection_mark.bounding_box,
-        selection_mark.confidence
-    ))
+form_pages = poller.result()
+
+for content in form_pages:
+    for table in content.tables:
+        print("Table found on page {}:".format(table.page_number))
+        print("Table location {}:".format(table.bounding_box))
+        for cell in table.cells:
+            print("Cell text: {}".format(cell.text))
+            print("Location: {}".format(cell.bounding_box))
+            print("Confidence score: {}\n".format(cell.confidence))
+
+    if content.selection_marks:
+        print("Selection marks found on page {}:".format(content.page_number))
+        for selection_mark in content.selection_marks:
+            print("Selection mark is '{}' within bounding box '{}' and has a confidence of {}".format(
+                selection_mark.state,
+                selection_mark.bounding_box,
+                selection_mark.confidence
+            ))
 ```
 
 ### Recognize Receipts