Add initial site prompt for csv.html

Created csv-site-prompt.md to outline requirements and design preferences for a new site at csv.html, referencing Dataplat.Dbatools.Csv and desired style inspirations.

Author: potatoqualitee

csv-site-prompt.md

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+i'd like to make a site at csv.html for my .net nuget Dataplat.Dbatools.Csv C:\github\dbatools.library\project\Dataplat.Dbatools.Csv
+
+Pls write it here at csv/ follow nuget webpage best practices plus make it web design best practices + beautiful and use font awesome if needed
+
+i like https://resend.com's style