chore(doc):Add more description to installing Gatsby-CLI globally (#21554)

* chore(doc):Add more description to installing Gatsby-CLI globally

* chore(doc):Add more description to installing Gatsby-CLI globally

* Update docs/docs/quick-start.md

Co-Authored-By: LB <[email protected]>

Co-authored-by: LB <[email protected]>

Author: Ekwuno

docs/docs/quick-start.md

@@ -19,6 +19,8 @@ This quick start is intended for intermediate to advanced developers. For a gent
 npm install -g gatsby-cli
 ```
 
+> The above command installs Gatsby CLI globally on your machine.
+
 ### Create a new site
 
 ```shell