docs: reword fallback option docs & validate sentence

Author: nekowinston

README.md

@@ -111,9 +111,9 @@ milliseconds. The value needs to be higher than the amount of milliseconds it
 takes to query your system for the dark mode state. Otherwise, you risk
 freezing neovim on shutdown.
 
-`fallback` specifies the theme to use when the auto-detection fails. This can
-be particularly useful to specify a default version when remotely connecting
-via SSH, or when using neovim on a tty.
+`fallback` specifies the appearance (`"dark" | "light"`) to use when the
+auto-detection fails. This can be particularly useful to specify a default
+version when remotely connecting via SSH, or when using neovim on a tty.
 
 ## 🚀 Usage
 

lua/auto-dark-mode/init.lua

@@ -25,7 +25,7 @@ local function validate_options(options)
 			function(opt)
 				return vim.tbl_contains({ "dark", "light" }, opt)
 			end,
-			"`fallback` must be either 'light' or 'dark'",
+			"`fallback` to be either 'light' or 'dark'",
 		},
 		set_dark_mode = { options.set_dark_mode, "function" },
 		set_light_mode = { options.set_light_mode, "function" },