Add an issue template for new features (#1163)

Author: foolip

.github/ISSUE_TEMPLATE /new-feature.yml

@@ -0,0 +1,26 @@
+name: New feature
+description: Suggest a new feature for web-features
+labels: feature definition
+body:
+- type: markdown
+  attributes:
+    value: |
+      Thanks for suggesting a new feature! Whether you suggest a feature here or by sending us a pull request, all contributions are welcome!
+
+      Please see our [contributing guidelines](https://github.com/web-platform-dx/web-features/blob/main/docs/CONTRIBUTING.md).
+- type: textarea
+  attributes:
+    label: Specification
+    description: Link to the spec for this feature
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Description
+    description: Describe the feature in one or two sentences.
+  validations:
+    required: true
+- type: textarea
+  attributes:
+    label: Browser support
+    description: If you have a caniuse.com link or other information about browser support, please share here.