add chat template to tokenizer_config.json

The current tokeniser uses the default (inappropriate) chat template.
This PR adds the correct chate template following https://github.com/chujiezheng/chat_templates.
You can find the easy-to-read version of the template at: https://github.com/chujiezheng/chat_templates/blob/main/chat_templates/falcon.jinja

tokenizer_config.json

@@ -8,5 +8,6 @@
   "model_max_length": 2048,
   "name_or_path": "tiiuae/falcon_tokenizer",
   "special_tokens_map_file": null,
-  "tokenizer_class": "PreTrainedTokenizerFast"
+  "tokenizer_class": "PreTrainedTokenizerFast",
+  "chat_template": "{% if messages[0]['role'] == 'system' %}{% set loop_messages = messages[1:] %}{% set system_message = messages[0]['content'] %}{% else %}{% set loop_messages = messages %}{% set system_message = '' %}{% endif %}{% for message in loop_messages %}{% if (message['role'] == 'user') != (loop.index0 % 2 == 0) %}{{ raise_exception('Conversation roles must alternate user/assistant/user/assistant/...') }}{% endif %}{% if loop.index0 == 0 %}{{ system_message.strip() }}{% endif %}{% if message['role'] == 'user' %}{{ '\n\nUser: ' + message['content'].strip().replace('\r\n', '\n').replace('\n\n', '\n') }}{% elif message['role'] == 'assistant' %}{{ '\n\nAssistant: ' + message['content'].strip().replace('\r\n', '\n').replace('\n\n', '\n') }}{% endif %}{% endfor %}{% if add_generation_prompt %}{{ '\n\nAssistant:' }}{% endif %}"
 }