Move lsp config to local file structure

.config/nvim/lsp/nickel_ls.lua

@@ -0,0 +1,32 @@
+---@brief
+---
+--- Nickel Language Server
+---
+--- https://github.com/tweag/nickel
+---
+--- `nls` can be installed with nix, or cargo, from the Nickel repository.
+--- ```sh
+--- git clone https://github.com/tweag/nickel.git
+--- ```
+---
+--- Nix:
+--- ```sh
+--- cd nickel
+--- nix-env -f . -i
+--- ```
+---
+--- cargo:
+--- ```sh
+--- cd nickel/lsp/nls
+--- cargo install --path .
+--- ```
+---
+--- In order to have lspconfig detect Nickel filetypes (a prerequisite for autostarting a server),
+--- install the [Nickel vim plugin](https://github.com/nickel-lang/vim-nickel).
+
+---@type vim.lsp.Config
+return {
+  cmd = { 'nls' },
+  filetypes = { 'ncl', 'nickel' },
+  root_markers = { '.git' },
+}