docs: create issue template

This will help enforce a minimum amount of necessary information, and
also help with automatic labeling.

.github/ISSUE_TEMPLATE/bug_report.yml

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+name: Bug Report
+description: Report a problem
+labels: [bug]
+body:
+  - type: textarea
+    attributes:
+      label: "Problem"
+      description: "Describe the current behavior. May include logs, images, or videos."
+    validations:
+      required: true
+
+  - type: textarea
+    attributes:
+      label: "Steps to reproduce"
+      placeholder: |
+        git clone --depth=1 https://github.com/tree-sitter/tree-sitter-ruby
+        cd tree-sitter-ruby
+        tree-sitter generate
+    validations:
+      required: true
+
+  - type: textarea
+    attributes:
+      label: "Expected behavior"
+      description: "Describe the behavior you expect."
+    validations:
+      required: true
+
+  - type: input
+    attributes:
+      label: "Tree-sitter version (tree-sitter --version)"
+      placeholder: "tree-sitter 0.20.9"
+    validations:
+      required: true
+
+  - type: input
+    attributes:
+      label: "Operating system/version"
+      placeholder: "macOS 11.5"
+    validations:
+      required: true

.github/ISSUE_TEMPLATE/config.yml

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+blank_issues_enabled: false

.github/ISSUE_TEMPLATE/feature_request.yml

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+name: Feature request
+description: Request an enhancement
+labels: [enhancement]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Before requesting: search [existing feature requests](https://github.com/tree-sitter/tree-sitter/labels/enhancement).
+
+  - type: textarea
+    attributes:
+      label: "Problem"
+      description: "Describe the problem to be solved."
+      placeholder: "No smurf icons available. Smurfs are useful because ..."
+    validations:
+      required: false
+
+  - type: textarea
+    attributes:
+      label: "Expected behavior"
+      description: "Describe what the new feature or behavior would look like. How does it solve the problem? Is it worth the cost?"
+    validations:
+      required: false