Neovim support (#31)

Summary:
`elp` works well with Neovim. `mason.nvim` is a very popular Neovim plugin for installing LSPs and linters, so I'd assume pretty much anyone using Neovim for programming has it installed. `mason.nvim` has `elp` in its registry so the installation is trivial.

Pull Request resolved: #31

Reviewed By: robertoaloi

Differential Revision: D57716927

Pulled By: alanz

fbshipit-source-id: b166fd4b695714087c3874c2f5b009c509ea6a58

website/docs/get-started/editors/neovim.md

@@ -0,0 +1,32 @@
+---
+sidebar_position: 4
+---
+
+# Neovim
+
+![screenshot](/img/neovim.png)
+
+The ELP project can be used as a [language server](https://microsoft.github.io/language-server-protocol/overviews/lsp/overview/) in Neovim.
+
+The easiest way to install the ELP server is to use [mason.nvim](https://github.com/williamboman/mason.nvim), a package manager
+focused on language servers, linters and similar tools. If you use Neovim for programming, you likely already have `mason.nvim` installed. It is also included in all the most popular "batteries included" configurations/distributions of Neovim such [kickstart.nvim](https://github.com/nvim-lua/kickstart.nvim), [LazyVim](https://github.com/LazyVim/LazyVim), [NVChad](https://nvchad.com/) and others.
+
+With `mason.nvim` installed, you can install the ELP server by running the following command:
+```
+:MasonInstall elp
+```
+from within Neovim.
+
+Alternatively you can run `:Mason` and browse the list of available packages, then press `i` when `elp` is highlighted.
+
+## Updating ELP
+
+You can update all packages managed by `mason.nvim` by running `:Mason` and pressing `U`.
+
+## Troubleshooting
+
+`:LspInfo` shows the current status of the LSP client.
+
+`:LspLog` opens the log file for the LSP client, which can be useful for debugging.
+
+