set fp16 to false if bf16, update bf16: auto in example YAMLs (#1122) [skip ci]

* set fp16 to false if bf16, update bf16: auto in example YAMLs

* unset fp16 so that it fallsback properly if bf16 isn't available

* Update README.md [skip-ci]

Co-authored-by: NanoCode012 <kevinvong@rocketmail.com>

* test that bf16 disables fp16

---------

Co-authored-by: NanoCode012 <kevinvong@rocketmail.com>

examples/yi-34B-chat/qlora.yml

@@ -7,8 +7,8 @@ load_in_8bit: false
 load_in_4bit: true
 strict: false
 sequence_len: 1024
-bf16: true
-fp16: false
+bf16: auto
+fp16:
 tf32: false
 flash_attention: true
 special_tokens: