minor #19474 [Frontend] Adding link to PostCSS (ThomasLandauer)

This PR was merged into the 6.4 branch.

Discussion
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[Frontend] Adding link to PostCSS

Commits
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7e70c66 [Frontend] Adding link to PostCSS

Author: javiereguiluz

frontend.rst

@@ -48,7 +48,7 @@ be executed by a browser.
 
 .. _ux-note-2:
 
-**[2]** There are some PostCSS plugins available to remove comments from CSS files.
+**[2]** There are some `PostCSS`_ plugins available to remove comments from CSS files.
 
 .. _frontend-asset-mapper:
 
@@ -115,3 +115,4 @@ Other Front-End Articles
 .. _Turbo: https://turbo.hotwired.dev/
 .. _Symfony UX: https://ux.symfony.com
 .. _API Platform: https://api-platform.com/
+.. _PostCSS: https://postcss.org/