Docs for customizing starting a dev server

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This section should mention show to use the `DEV_PORT` env and also how the `config/watch.yml` works.
https://luckyframework.org/guides/getting-started/starting-project#start-the-server

To change your port or host, you update your `config/watch.yml`, but if you use `overmind` or other such process runners, these use `PORT` which causes your `config/watch.yml` to be ignored, so you need to use `DEV_PORT` or `DEV_HOST` env. However, because the `.env` file isn't read until runtime, you need the `DEV_PORT` and `DEV_HOST` values to exist before compile time which means they need to be specified in the CLI (e.g. `DEV_PORT=3004 lucky dev`)

Start with the “Start the server” section at the linked getting-started guide and review how config/watch.yml is described. Document DEV_PORT and DEV_HOST, including their interaction with PORT-based process runners and the need to provide values on the lucky dev command line before compilation. Done means the guide explains both configuration paths and their precedence.

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