stow: Split systemd package into bspwm and ssh-agent

Since urxvt will only be used on my bspwm setup, and since ssh-agent
can be used on non-bspwm setups as well, it makes sense to separate
the two.

ssh-agent/.config/systemd/user/ssh-agent.service

@@ -0,0 +1,10 @@
+[Unit]
+Description=SSH agent
+
+[Service]
+Type=forking
+Environment=SSH_AUTH_SOCK=%t/ssh-agent.socket
+ExecStart=/usr/bin/ssh-agent -a $SSH_AUTH_SOCK
+
+[Install]
+WantedBy=default.target

ssh-agent/README.md

@@ -0,0 +1,23 @@
+# ssh-agent
+
+SSH is used to connect to remote machines. I use a systemd service to manage ssh-agent.
+
+## Dependencies
+
+- [openssh][openssh] - SSH support
+
+## Installation
+
+```sh
+make package=ssh-agent
+```
+
+## Usage
+
+```sh
+systemctl --user enable --now ssh-agent.service
+```
+
+In order for ssh-agent to cache your keys, you must first add them with `ssh-add`.
+
+[openssh]: https://www.archlinux.org/packages/core/x86_64/openssh/