Add luacheckrc for neovim

.luacheckrc

@@ -0,0 +1,24 @@
+-- vim: expandtab:shiftwidth=2:tabstop=2:softtabstop=2:textwidth=80
+
+-- Only allow symbols available in all Lua versions
+std = "luajit"
+
+-- Get rid of "unused argument self"-warnings
+self = false
+
+-- This file itself
+files[".luacheckrc"].ignore = {"111", "112", "131"}
+
+-- Rerun tests only if their modification time changed.
+cache = false
+
+ignore = {
+  "212", -- Unused argument, In the case of callback function, _arg_name is easier to understand than _, so this option is set to off.
+  "631", -- max_line_length, vscode pkg URL is too long
+}
+
+-- Global objects defined by the C code
+globals = {
+  "vim",
+  "use"
+}