chore(docs): Add new language in transalation list (#19467)

* Add Gujarati, French, Mongolian langulage to new transalation list

* Add the entries alphabetically sorted by the language code

docs/contributing/gatsby-docs-translation-guide.md

@@ -31,10 +31,13 @@ The first step for starting a new translation is to check what exists. So far, t
 - [Arabic](https://github.com/gatsbyjs/gatsby-ar)
 - [German](https://github.com/gatsbyjs/gatsby-de)
 - [Spanish](https://github.com/gatsbyjs/gatsby-es)
+- [French](https://github.com/gatsbyjs/gatsby-fr)
+- [Gujarati](https://github.com/gatsbyjs/gatsby-gu)
 - [Hindi](https://github.com/gatsbyjs/gatsby-hi)
 - [Indonesian](https://github.com/gatsbyjs/gatsby-id)
 - [Italian](https://github.com/gatsbyjs/gatsby-it)
 - [Korean](https://github.com/gatsbyjs/gatsby-ko)
+- [Mongolian](https://github.com/gatsbyjs/gatsby-mn)
 - [Dutch](https://github.com/gatsbyjs/gatsby-nl)
 - [Polish](https://github.com/gatsbyjs/gatsby-pl)
 - [Brazilian Portuguese](https://github.com/gatsbyjs/gatsby-pt-BR)