Define headless CMS at start of article (#17455)
Define headless CMS at start of article (#17455)

* Define headless CMS at start of article

* chore: format

* Remove "web" from "web developers" - docs/docs/headless-cms.md

Co-Authored-By: Kyle Gill <94ae90b5a2cda186efc52272b2c47c78482de269@gmail.com>

* Update docs/docs/headless-cms.md

Co-Authored-By: Marcy Sutton <63f38fb7a2c9e72439a06d93cefb66621e8fc496@gatsbyjs.com>

* Update docs/docs/headless-cms.md

Co-Authored-By: Marcy Sutton <63f38fb7a2c9e72439a06d93cefb66621e8fc496@gatsbyjs.com>

* Update headless-cms.md

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