[Docs] Add issue template (#113)

### What this PR does / why we need it?
Add issue templates.

Most of templates in this PR are from vllm-project/vllm:
https://github.com/vllm-project/vllm/tree/main/.github/ISSUE_TEMPLATE

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?

Test on my local repo by setting default branch to ISSUE_TEMPLATE:
https://github.com/Yikun/vllm-ascend/issues

https://github.com/Yikun/vllm-ascend/issues/new/choose

Closes: https://github.com/vllm-project/vllm-ascend/issues/48

---------

Signed-off-by: Yikun Jiang <yikunkero@gmail.com>

.github/ISSUE_TEMPLATE/600-new-model.yml

@@ -0,0 +1,33 @@
+name: 🤗 Support request for new model supported from huggingface/modelscope/modelers on Ascend
+description: Submit a proposal/request for a new model from huggingface/modelscope/modelers on Ascend
+title: "[New Model]: "
+labels: ["new model"]
+
+body:
+- type: markdown
+  attributes:
+    value: >
+      #### Before submitting an issue, please make sure the issue hasn't been already addressed by searching through [the existing and past issues](https://github.com/vllm-project/vllm-ascend/issues?q=is%3Aissue+sort%3Acreated-desc+).
+
+      #### We also highly recommend you read https://vllm-ascend.readthedocs.io/en/latest/user_guide/supported_models.html first to know which model already supported.
+- type: textarea
+  attributes:
+    label: The model to consider.
+    description: >
+      A huggingface/modelscope/modelers url, pointing to the model, e.g. https://huggingface.co/openai-community/gpt2 .
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: The closest model vllm already supports.
+    description: >
+      Here is the list of models already supported by vllm: https://vllm-ascend.readthedocs.io/en/latest/user_guide/supported_models.html . Which model is the most similar to the model you want to add support for?
+- type: textarea
+  attributes:
+    label: What's your difficulty of supporting the model you want?
+    description: >
+      For example, any new operators or new architecture?
+- type: markdown
+  attributes:
+    value: >
+      Thanks for contributing 🎉!