docs: add local development and CI guide to template docs (#2)

[AbhiLohar]

This PR addresses the "Fundamental Documentation" task in Issue #2.
While the template previously had documentation for the "server-side" (GitHub Actions and PyPI), it lacked guidance for the Developer Experience.

What's New:

Added a Local Development Workflow section to {{ cookiecutter.package_name }}/docs/ci.rst.
Documented pre-commit hooks, specifically explaining how to handle Mixed Line Endings (LF) and trailing whitespace.
Added instructions for using Tox to run style checks (tox -e codestyle) and tests locally.
Fixed YAML indentation and formatting in the existing CI examples to ensure a clean build.

This ensures that every new package created with this template will have clear instructions for its contributors from day one.

[AbhiLohar]

Hi @Cadair,I've added the fundamental CI and local development documentation to the template as discussed in #2. Please, correct me if any changes is required, for that i am adding this as Draft PR.

Thank you!