Add tutorial for converting existing projects

[joematthews]

I am thinking about including a markdown tutorial of how to add the schematics, packages, and configs to an existing Angular project.

• cross link to existing configuration files to save time and prevent duplicate information
• add new lint:summary and lint:style:summary scripts that show a count of errors/warnings per rule
  • I've used eslint-formatter-summary for this in the past, but I fear it may not be compatible with eslint 9.