[Bugfix] Set ACL_OP_INIT_MODE env var default to 0 (#1123)

### What this PR does / why we need it?

Set `ACL_OP_INIT_MODE` env var default to `0`, since vllm-ascend may
have problems in some scenarios when setting it to `1`.

Plus, the guide #734
has also been updated.

Signed-off-by: shen-shanshan <467638484@qq.com>

Author: shen-shanshan

vllm_ascend/envs.py

@@ -127,7 +127,7 @@
     # We set this var default to `1` in vllm-ascend to avoid segment fault when
     # enable `pin_memory` while creating a tensor using `torch.tensor`.
     "VLLM_ASCEND_ACL_OP_INIT_MODE":
-    lambda: os.getenv("VLLM_ASCEND_ACL_OP_INIT_MODE", '1'),
+    lambda: os.getenv("VLLM_ASCEND_ACL_OP_INIT_MODE", '0'),
     # Some models are optimized by vllm ascend. While in some case, e.g. rlhf
     # training, the optimized model may not be suitable. In this case, set this
     # value to False to disable the optimized model.