(blog)Add challenge 5 of 100DaysOfGatsby (#20958)
(blog)Add challenge 5 of 100DaysOfGatsby (#20958)

* Add challenge 5 of 100DaysOfGatsby

* Update docs/blog/100days/mdx/index.md

Co-Authored-By: LB <215e3d7c445b99629add69586ce9b88253e8211e@gmail.com>

* Update docs/blog/100days/mdx/index.md

Co-Authored-By: LB <215e3d7c445b99629add69586ce9b88253e8211e@gmail.com>

* Remove reference to WordPress shortcodes

* chore: format

Co-authored-by: LB <8468275f0d120527324004754c3d088324306866@gatsbyjs.com>
Co-authored-by: GatsbyJS Bot <313a651c59fdaade90d152972001707d94b0975c@gmail.com>

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