Layout for llmstxt

[danielwagn3r]

I suggest to add a layout for llmstxt, as proposed here https://llmstxt.org/, to Blowfish.

Before migrating to Blowfish, I used thehugo-PaperMod theme, which already has implemented such a layout with adityatelange/hugo-PaperMod@3bb0ca2.

I've ported the code to Blowfish, which was easy and prepared a branch of my fork https://github.com/danielwagn3r/blowfish/tree/llmstxt which could be PRed here #2788