README: add documentation

Fixes GH-3

1 files changed, 54 insertions, 1 deletions

diff --git a/README.md b/README.md
index f4440aa..28d565b 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,57 @@
 pacman-offline
 ==============
 
-Run offline system update with pacman.
+**Run offline system update with pacman.**
+
+The offline system update with pacman is achieved by integrating into
+[offline updates in systemd](https://www.freedesktop.org/software/systemd/man/systemd.offline-updates.html#/etc/system-update).
+In fact only two scripts and a number of systemd unit files are used to
+glue `systemd` and `pacman`.
+
+Requirements
+------------
+
+There are the runtime dependencies:
+
+* [pacman](https://archlinux.org/pacman/)
+* [systemd](https://www.github.com/systemd/systemd)
+
+Optional basic support for
+[plymouth](https://www.freedesktop.org/wiki/Software/Plymouth/) is
+integrated.
+
+Usage
+-----
+
+A single command `pacman-offline` is used to prepare the offline update.
+It accepts some arguments:
+
+* *-c*: clean before download
+* *-f*: force if other system-update is pending
+* *-h*: show help
+* *-r*: reboot and install immediately
+* *-t*: start timer for nightly reboot
+* *-y*: update sync databases
+
+Configuration
+-------------
+
+A sinppet for inclusion in `/etc/pacman.conf` is shipped. To make use of
+it add this line:
+
+    Include = /etc/pacman.d/offline.conf
+
+It will cause `pacman` to ignore linux packages and prevent breaking module
+loading. These packages are not ignored on offline update.
+
+Modify `/etc/pacman.d/offline.conf` to your needs by changing or adding
+packages.
+
+### Upstream
+
+URL:
+[GitHub.com](https://github.com/eworm-de/pacman-offline#pacman-offline)
+
+Mirror:
+[eworm.de](https://git.eworm.de/cgit.cgi/pacman-offline/)
+[GitLab.com](https://gitlab.com/eworm-de/pacman-offline#pacman-offline)