Add readme

Signed-off-by: Marko Korhonen <marko.korhonen@reekynet.com>

README.md

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+# LiQuid Screen Dim
+A simple utility which dims your screen. It saves the previous brightness too, so you can restore to the point before dimming.
+
+## Why Rust?
+I wanted start a small project to learn Rust. Before this, I was using [this script]("https://github.com/Bonnee/dotfiles/blob/wayland/scripts/bin/dim.sh") and figured, why not rewrite it in Rust.
+
+## Usage
+```
+USAGE:
+    lqsd [FLAGS] [OPTIONS]
+
+FLAGS:
+    -d, --dim        Dims the screen to idle level set in configuration
+    -h, --help       Prints help information
+    -r, --resume     Sets the backlight to the value it was before dimming
+    -V, --version    Prints version information
+
+OPTIONS:
+    -c, --config <config>    Sets a custom config file
+```
+The configuration file resides at `$XDG_CONFIG_HOME/lqsd/config.toml`. There you can set these values:
+
+`resume_file_path`: the location where the previous brightness is saved (default: `/tmp/lqsd-resume`)
+
+`idle_level`: the minimum brightness that will be dimmed to. Can be a value between 0-100 (default 0)
+
+`dim_speed`: this sets the "sleep time" between each backlight command. It's in milliseconds (default 50)
+
+`resume_speed`: same as the last one, only for the resume operation `-r` (default 25)