👌 copier.yml: Exclude scaffold files from copier update

README.md, docs/index.md, and the package __init__.py are minimal scaffolds that users
customize early. Overwriting them on `copier update` would discard those changes. Add all
three to `_exclude`, matching the existing pattern for tests/ and CHANGELOG.md.

Author: mbercx

copier.yml

@@ -37,3 +37,6 @@ _message_after_copy: |
 _exclude:
     - "{% if _copier_operation == 'update' -%}tests{% endif %}"
     - "{% if _copier_operation == 'update' -%}CHANGELOG.md{% endif %}"
+    - "{% if _copier_operation == 'update' -%}README.md{% endif %}"
+    - "{% if _copier_operation == 'update' -%}docs/index.md{% endif %}"
+    - "{% if _copier_operation == 'update' -%}src/{{ package_name.lower().replace('-', '_') }}/__init__.py{% endif %}"