[readme] add useful readme

Author: winksplorer

README.md

@@ -1,2 +1,34 @@
-# yabnt
-Yet Another Battery Notification Thing
+# yabnt - yet another battery notification thing
+
+a stupidly simple piece of code that uses libnotify to create notifications based on your battery level.
+
+## behaviors
+
+### battery% > 10%
+
+exits immediately, no notification.
+
+### battery% <= 10%
+
+creates low battery warning notification with normal urgency
+
+### battery% <= 5%
+
+creates low battery warning notification with critical urgency
+
+## build & installation
+
+1. clone repo `git clone https://github.com/winksplorer/yabnt`
+2. install deps, for debian this is `sudo apt install clang libnotify-dev`
+3. build `make`
+4. install `sudo make install`
+
+## setting up with cron
+
+you can use yabnt with cron to automatically give you warnings.
+
+this example runs yabnt every minute, with messages to /tmp/yabnt.log.
+
+```
+* * * * * DISPLAY=:0 yabnt >/tmp/yabnt.log 2>&1
+```