Update README with project initialization instructions (#1772)

* Update README with project initialization instructions

Added instructions for creating a new project and initializing in an existing project.

* Update README.md with alternative one-time usage command for existing projects

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Added --ai option to prevent interactive AI selection

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>