[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/100-documentation.yml

@@ -0,0 +1,22 @@
+name: 📚 Documentation
+description: Report an issue related to https://vllm-ascend.readthedocs.org
+title: "[Doc]: "
+labels: ["documentation"]
+
+body:
+- type: textarea
+  attributes:
+    label: 📚 The doc issue
+    description: >
+      A clear and concise description of what content in https://vllm-ascend.readthedocs.org/ is an issue.
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Suggest a potential alternative/fix
+    description: >
+      Tell us how we could improve the documentation in this regard.
+- type: markdown
+  attributes:
+    value: >
+      Thanks for contributing 🎉!