docs: Update gatsby-cli ReadMe for develop PORT env var (#20417)
docs: Update gatsby-cli ReadMe for develop PORT env var (#20417)

* Update gatsby-cli ReadMe for develop PORT env var 

Updates reference not caught in #20250

* chore: format

Co-authored-by: GatsbyJS Bot <313a651c59fdaade90d152972001707d94b0975c@gmail.com>

gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby