Add tags to example data and improve docs (for gunthercox#2409)

Author: gunthercox

docs/training.rst

@@ -139,6 +139,8 @@ Training with CSV or TSV formatted data
 .. autoclass:: chatterbot.trainers.CsvFileTrainer
    :members: train
 
+   .. autoattribute:: chatterbot.trainers.CsvFileTrainer.DEFAULT_STATEMENT_TO_HEADER_MAPPING
+
 
 Example CSV data format:
 
@@ -169,6 +171,8 @@ Training with JSON formatted data
 .. autoclass:: chatterbot.trainers.JsonFileTrainer
    :members: train
 
+   .. autoattribute:: chatterbot.trainers.JsonFileTrainer.DEFAULT_STATEMENT_TO_KEY_MAPPING
+
 
 Example JSON data format:
 

tests/training/test_data/json_corpus/1.json

@@ -4,13 +4,19 @@
             "text": "Hello",
             "in_response_to": null,
             "persona": "user 1",
-            "conversation": "test"
+            "conversation": "test",
+            "tags": [
+                "greeting"
+            ]
         },
         {
             "text": "Is anyone there?",
             "in_response_to": "Hello",
             "persona": "user 1",
-            "conversation": "test"
+            "conversation": "test",
+            "tags": [
+                "question"
+            ]
         },
         {
             "text": "Yes",