docs: document remote Docker host for local development (#692)

* docs: document remote Docker and BuildKit setup for local development

Generated-by: aiautocommit

* chore: ignore local mise configuration file

Generated-by: aiautocommit

* docs(guides): explain why to use a remote Docker host

Generated-by: aiautocommit

* docs(config): update environment variables documentation

- Document how Railpack reads environment variables from its process environment
- Relocate and update description for `RAILPACK_DISABLE_CACHES`
- Fix table formatting and minor phrasing

Generated-by: aiautocommit

* docs: clarify remote docker host guide for local development

Generated-by: aiautocommit

* docs: update BuildKit setup instructions to use docker command

Generated-by: aiautocommit