docs: fix typo in template README contributing section

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016ZE2P69fGRrf2vbcbWjVBH

Author: tsvikas

project_name/README.md.jinja

@@ -55,7 +55,7 @@ Use `{{ project_name }} --help` to learn more.
 ## Contributing
 
 Interested in contributing?
-See [CONTRIBUTING.md](CONTRIBUTING.md) for development setup and guideline.
+See [CONTRIBUTING.md](CONTRIBUTING.md) for development setup and guidelines.
 
 {% if format_tool == "black" -%}
 [black-badge]: https://img.shields.io/badge/code%20style-black-000000.svg