Re-add Neovim configuration files

Re-included from https://github.com/opdavies/opdavies.nvim.

config/neovim/plugin/colorscheme.lua

@@ -0,0 +1,25 @@
+local status_ok, catppuccin = pcall(require, "catppuccin")
+if not status_ok then
+  return
+end
+
+catppuccin.setup {
+  flavour = "macchiato",
+  integrations = {
+    cmp = true,
+    gitsigns = true,
+    mini = {
+      enabled = true,
+      indentscope_color = "",
+    },
+    native_lsp = {
+      enabled = true,
+    },
+    telescope = true,
+    treesitter = true,
+  },
+  term_colors = true,
+  transparent_background = true,
+}
+
+vim.cmd.colorscheme "catppuccin"