[DOC] add issue template

.github/ISSUE_TEMPLATE/bug-report.yml

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+name: "\U0001F41B Bug Report"
+description: Submit a bug report to help us improve learnware
+body:
+  - type: textarea
+    id: system-info
+    attributes:
+      label: System Info
+      description: Please share your system info with us.
+      placeholder: learnware version, platform, python version, ...
+    validations:
+      required: true
+
+  - type: textarea
+    id: reproduction
+    validations:
+      required: true
+    attributes:
+      label: Reproduction
+      description: |
+        Please provide a code sample that reproduces the problem you ran into. It can be a Colab link or just a code snippet.
+        If you have code snippets, error messages, stack traces please provide them here as well.
+        Important! Use code tags to correctly format your code. See [Github Guidelines about Code Blocks](https://help.github.com/en/github/writing-on-github/creating-and-highlighting-code-blocks#syntax-highlighting).
+        Do not use screenshots, as they are hard to read and (more importantly) don't allow others to copy-and-paste your code.
+
+      placeholder: |
+        Steps to reproduce the behavior:
+          
+          1.
+          2.
+          3.
+          
+  - type: textarea
+    id: expected-behavior
+    validations:
+      required: true
+    attributes:
+      label: Expected behavior
+      description: "A clear and concise description of what you would expect to happen."

.github/ISSUE_TEMPLATE/documentation.yml

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+name: "\U0001F4D6 Documentation"
+description: Report an issue related to documentation
+labels: [ "documentation" ]
+body:
+  - type: textarea
+    id: description
+    validations:
+      required: true
+    attributes:
+      label: Description
+      description: |
+        A clear description of the issue related to documentation.

.github/ISSUE_TEMPLATE/feature-request.yml

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+name: "\U0001F680 Feature request"
+description: Submit a proposal/request for a new learnware feature
+labels: [ "feature" ]
+body:
+  - type: textarea
+    id: feature-request
+    validations:
+      required: true
+    attributes:
+      label: Feature request
+      description: |
+        A clear and concise description of the feature proposal. Please provide a link to the paper and code in case they exist.
+
+  - type: textarea
+    id: motivation
+    validations:
+      required: true
+    attributes:
+      label: Motivation
+      description: |
+        Please outline the motivation for the proposal. Is your feature request related to a problem? e.g., I'm always frustrated when [...]. If this is related to another GitHub issue, please link here too.
+
+  - type: textarea
+    id: contribution
+    validations:
+      required: true
+    attributes:
+      label: Your contribution
+      description: |
+        Is there any way that you could help, e.g. by submitting a PR? Make sure to read the [developer guide](https://github.com/Learnware-LAMDA/Learnware/blob/main/docs/about/dev.rst).

.github/ISSUE_TEMPLATE/question.yml

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+name: "\U00002753 Questions & Help"
+description: Have some questions? We can offer help
+labels: [ "question" ]
+body:
+  - type: textarea
+    id: question
+    validations:
+      required: true
+    attributes:
+      label: Description
+      description: |
+        We sincerely suggest you to carefully read the [documentation](http://learnware.readthedocs.io/) of our library. After that, if you still feel puzzled, please describe the question clearly under this issue.