add: luacheck

.luacheckrc

@@ -0,0 +1,38 @@
+-- Only allow symbols available in all Lua versions
+std = "min"
+
+-- Get rid of "unused argument self"-warnings
+self = false
+
+-- Global objects defined by the C code
+read_globals = {
+    "awesome",
+    "button",
+    "dbus",
+    "drawable",
+    "drawin",
+    "key",
+    "keygrabber",
+    "mousegrabber",
+    "selection",
+    "tag",
+    "window",
+    "table.unpack",
+    "math.atan2",
+}
+
+-- screen may not be read-only, because newer luacheck versions complain about
+-- screen[1].tags[1].selected = true.
+-- The same happens with the following code:
+--   local tags = mouse.screen.tags
+--   tags[7].index = 4
+-- client may not be read-only due to client.focus.
+globals = {
+    "screen",
+    "mouse",
+    "root",
+    "client"
+}
+
+-- Enable cache (uses .luacheckcache relative to this rc file).
+cache = true