Add readme information with usage and overview

README.md

@@ -0,0 +1,36 @@
+## Systemd User SSH PAM
+
+This script has a rather specific use case. If you fit the following demographic
+then this script might just be for you!
+
+ * You use systemd as a user session manager (either
+   [this](https://github.com/sofar/user-session-units), or [this](https://github.com/EvanPurkhiser/systemd-user-sessions)
+ * You have a `systemd --user` service called `ssh-agent.service` that starts
+   your ssh agent.
+ * You hav to type your password a second time after logging in in order to
+   decrypt your SSH key.
+
+This script lets you only type your password one, both logging you in and
+decrypting your ssh key and adding it to your agent.
+
+## Usage
+
+There are a few pre-requisits to this script:
+
+ 1. Your systemd --user session needs to be started during login time. This wont
+    be a problem if you use one of the user-session services mentioned above.
+ 2. Your systemd --user instance needs to know about the SSH_AUTH_SOCK. If
+    you're using my systemd-user-sessions package mentioned abouve then you will
+    want to add this to your `~/.config/bash/environment` file as something like
+    `SSH_AUTH_SOCK=$XDG_RUNTIME_DIR/ssh-agent`
+
+To enable the script you will want to add this to your pam configuration
+(probably `/etc/pam.d/system-login` or `/etc/pam.d/login`
+
+    auth  optional  pam_exec.so  expose_authtok /path/to/the/systemd-user-pam-ssh
+
+## Installation
+
+I would recomend placing the script under `/usr/lib/systemd/`. If you are using
+Arch Linux you can use the PKGBUILD [located
+here](https://github.com/EvanPurkhiser/PKGBUILDs/tree/master/systemd-user-pam-ssh-git)