Meta: update repository files

See https://github.com/whatwg/spec-factory for details.

Author: annevk

.github/ISSUE_TEMPLATE/0-new-issue.yml

@@ -0,0 +1,17 @@
+name: New issue
+description: File a new issue against the HTML Standard.
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Before filling out this form, please familiarize yourself with the [Code of Conduct](https://whatwg.org/code-of-conduct). You might also find the [FAQ](https://whatwg.org/faq) and [Working Mode](https://whatwg.org/working-mode) useful.
+
+        If at any point you have questions, please reach out to us on [Chat](https://whatwg.org/chat).
+  - type: textarea
+    attributes:
+      label: "What is the issue with the HTML Standard?"
+    validations:
+      required: true
+  - type: markdown
+    attributes:
+      value: "Thank you for taking the time to improve the HTML Standard!"

.github/ISSUE_TEMPLATE/1-new-feature.yml

@@ -0,0 +1,27 @@
+name: New feature
+description: Request a new feature in the HTML Standard.
+labels: ["addition/proposal", "needs implementer interest"]
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Before filling out this form, please familiarize yourself with the [Code of Conduct](https://whatwg.org/code-of-conduct), [FAQ](https://whatwg.org/faq), and [Working Mode](https://whatwg.org/working-mode). They help with setting expectations and making sure you know what is required. The FAQ ["How should I go about proposing new features to WHATWG standards?"](https://whatwg.org/faq#adding-new-features) is especially relevant.
+
+        If at any point you have questions, please reach out to us on [Chat](https://whatwg.org/chat).
+  - type: textarea
+    attributes:
+      label: "What problem are you trying to solve?"
+    validations:
+      required: true
+  - type: textarea
+    attributes:
+      label: "What solutions exist today?"
+  - type: textarea
+    attributes:
+      label: "How would you solve it?"
+  - type: textarea
+    attributes:
+      label: "Anything else?"
+  - type: markdown
+    attributes:
+      value: "Thank you for taking the time to improve the HTML Standard!"

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,8 @@
+blank_issues_enabled: false
+contact_links:
+  - name: Chat
+    url: https://whatwg.org/chat
+    about: Please do reach out with questions and feedback!
+  - name: Stack Overflow
+    url: https://stackoverflow.com/
+    about: If you're having trouble building a web page, this is not the right repository. Consider asking your question on Stack Overflow instead.

PULL_REQUEST_TEMPLATE.md

@@ -1,18 +1,21 @@
 <!--
 Thank you for contributing to the HTML Standard! Please describe the change you are making and complete the checklist below if your change is not editorial.
+When editing this comment after the PR is created, check that PR-Preview doesn't overwrite your changes.
+If you think your PR is ready to land, please double-check that the build is passing and the checklist is complete before pinging.
 -->
 
 - [ ] At least two implementers are interested (and none opposed):
    * …
    * …
 - [ ] [Tests](https://github.com/web-platform-tests/wpt) are written and can be reviewed and commented upon at:
-   * …
+   * … <!-- If these tests are tentative, link a PR to make them non-tentative. -->
 - [ ] [Implementation bugs](https://github.com/whatwg/meta/blob/main/MAINTAINERS.md#handling-pull-requests) are filed:
    * Chromium: …
    * Gecko: …
    * WebKit: …
    * Deno (only for timers, structured clone, base64 utils, channel messaging, module resolution, web workers, and web storage): …
    * Node.js (only for timers, structured clone, base64 utils, channel messaging, and module resolution): …
 - [ ] [MDN issue](https://github.com/whatwg/meta/blob/main/MAINTAINERS.md#handling-pull-requests) is filed: …
+- [ ] The top of this comment includes a [clear commit message](https://github.com/whatwg/meta/blob/main/COMMITTING.md) to use. <!-- If you created this PR from a single commit, Github copied its message. Otherwise, you need to add a commit message yourself. -->
 
 (See [WHATWG Working Mode: Changes](https://whatwg.org/working-mode#changes) for more details.)