Add documentation for Language Server Support

Without Node installed, the language server plugin is throwing errors on startup, hence we must first check if node is available or not and if it is not available, we must show the user a meaningful error. Also we must mention in the documentation that for language server support, using [coc.nvim](https://github.com/neoclide/coc.nvim), node must be installed on the system.

Start by finding the language server support path in the Neovim plugin and the documentation section that describes coc.nvim usage. Reproduce startup without Node installed, then the work is done when the plugin shows a meaningful missing-Node error and the docs state that Node is required for language server support.

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