Add documentation

README.md

@@ -1,3 +1,29 @@
 # upcheck
 
-Check ArchLinux available updates and send it via libnotify.
+Check ArchLinux available updates and send it via libnotify.
+
+# How to install and get it working?
+
+First install [pacman-contrib](https://www.archlinux.org/packages/community/x86_64/pacman-contrib/) and [libnotify](https://www.archlinux.org/packages/extra/x86_64/libnotify/) from ArchLinux repos:
+
+```
+# pacman -Syu --needed pacman-contrib libnotify
+```
+
+Installation is easy, put the `upcheck` script in $HOME/.local/bin/, then put the `upcheck.service` and `upcheck.timer` into $HOME/.config/systemd/user/ and enable/start `upcheck.timer` with the command `systemctl --user enable upcheck.timer && systemctl --user start upcheck.timer`
+
+**Important note**: you need a [notifications server](https://wiki.archlinux.org/index.php/Desktop_notifications#Notification_servers) if you aren't using Cinnamon, Deepin, Enlightenment, GNOME, GNOME Flashback or KDE Plasma.
+
+# How it works?
+
+It use the `checkupdates` bash script provided by the `pacman-contrib` package and the `notify-send` binary provided by the `libnotify` package. First, it exec the command `checkupdates` and save the output in a variable, if the variable is not an empty string, mean that there are available updates and then send the variable content using `libnotify`.
+
+# What is the purpose?
+
+It doesn't have any special purpose, it was created only trying to avoid the user manual interaction of checking available updates everytime and show it when are available.
+
+# How can I checge the execution frequency time?
+
+Modify the `upcheck.timer` unit and change the OnUnitActiveSec= option to what you want. See `man 7 systemd.time` for the time specifications.
+
+That is all.