Update README.md

Author: thiagogq

README.md

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 # LibreBlog
 
 **LibreBlog** is an in-browser static site generator that supports Markdown, RIS references, and image embedding to create content-rich blogs. There are different types of articles, each with its own features.
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+The site is available at <https://editor2.libreblog.org/LibreBlog/> — a mirror of the GitHub Pages site (<https://libreblogorg.github.io/LibreBlog/>). GitHub Pages doesn’t support the COOP/COEP headers required for proper operation.
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 ![LaTeX](https://raw.githubusercontent.com/LibreBlogOrg/LibreBlog-Resources/refs/heads/main/screenshots/latex.avif)