🔧 Add an explicit Chronographer config

In particular, this allows setting up hints for leading the
contributors to the docs that explain the changelog fragments
expectations. This allows having the preferences documented as code.

.github/chronographer.yml

@@ -0,0 +1,23 @@
+---
+
+action-hints:
+  # check-title-prefix: chng  # default: `{{ branch-protection-check-name }}: `
+  external-docs-url: https://pip.pypa.io/how-to-changelog
+  inline-markdown: >
+    Check out https://pip.pypa.io/how-to-changelog
+
+branch-protection-check-name: Timeline protection
+
+enforce-name:
+  # suffix: .md
+  suffix: .rst
+
+exclude:
+  bots:
+  - dependabot-preview
+  - dependabot
+  - patchback
+  humans:
+  - pyup-bot
+
+...