Add Estonian language to Neovim spellchecker

How to generate the necessary language files:
- install hunspell-et on Arch Linux
- run `nvim -u NONE -c "mkspell! et /usr/share/hunspell/et_EE" -c q` in ~/.local/share/nvim/site/spell

dot_config/nvim/lua/wekuz/executable_opts.lua

@@ -19,4 +19,4 @@ vim.opt.undofile = true
 vim.opt.updatetime = 2000
 
 vim.opt.clipboard = "unnamedplus"
-vim.opt.spelllang = { "en_gb", "en_us" }
+vim.opt.spelllang = { "en_gb", "en_us", "et" }