Document installation for Emacs

[liar666]

Hi,

It would be great if the main page README would be a little more explicit on how to install in Emacs.

For the moment it just points to lsp page, which gives absolutely no hint about R-languageserver...

Thanks to #44 (comment) , I discovered that the lines to add to the config file must be something like:

(package-initialize)
(require 'eglot)
(require 'ess-site)
(add-hook 'ess-r-mode-hook 'eglot-ensure)

Would be great it they are verified & added to the main page "Emacs" section.

[randy3k]

You are welcome to contribute a pull request for better documentation. It would be best written by someone who has the corresponding experience.