feat: add render-markdown.nvim integration

[ValdezFOmar]

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feat: add render-markdown.nvim integration
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[ValdezFOmar]

I used the name render_markdown since there's already a markdown integration, but still tried to clarify in the README that the actual plugin is markdown.nvim.

[vollowx]

Maybe markdown_nvim?

[ValdezFOmar]

The plugin suggests in its README the use of the name render-markdown to avoid collisions with other plugins, the actual package uses the same name and the highlight groups and commands use RenderMarkdown as a prefix, so maybe is ok?

[vollowx]

Makes sense