Improve unit files, add binary install to README

After going through the process of getting this working using the unit
files, I found a few issues that are fixed here.

README.md

@@ -19,6 +19,14 @@ and freedom.
 * Git 2.34 or later
 * OpenSSH 9.1 or later with `ssh-agent`
 
+### 📀 From binaries
+
+> Requires `curl` and `tar`.
+
+Run the following command to install the latest binary release:
+
+    sh <(curl -sSf https://radicle.xyz/install)
+
 ### 📦 From source
 
 > Requires the Rust toolchain.

radicle-httpd/radicle-httpd.service

@@ -0,0 +1,28 @@
+# Example systemd unit file for `radicle-httpd`.
+#
+# When running radicle-httpd on a server, it should be run as a separate user.
+#
+# Copy this file into /etc/systemd/system and set the User/Group parameters
+# under [Service] appropriately.
+#
+# For users wishing to run a configured version of the service, copy this
+# service file into the user's systemd directory, and edit appropriately.
+#
+# For example:
+#
+#   mkdir -p $HOME/.config/systemd/user/
+#   cp radicle-node.service $HOME/.config/systemd/user/radicle-node.service
+#
+[Unit]
+After=syslog.target network.target
+Description=Radicle HTTPd
+
+[Service]
+ExecStart=%h/.radicle/bin/radicle-httpd
+Environment=RAD_HOME=%h/.radicle
+KillMode=process
+Restart=always
+RestartSec=1
+
+[Install]
+WantedBy=default.target

radicle-node/radicle-node.service

@@ -1,27 +1,36 @@
+# Example systemd unit file for `radicle-node`.
+#
 # When running radicle-node on a server, it should be run as a separate user.
+#
 # Copy this file into /etc/systemd/system and set the User/Group parameters
 # under [Service] appropriately.
-
+#
 # For users wishing to run a configured version of the service, copy this
 # service file into the user's systemd directory, and edit appropriately.
 #
-#   mkdir -p $HOME/.local/share/systemd/user/
+# For example:
-#   cp radicle-node.service $HOME/.local/share/systemd/user/radicle-node.service
 #
-# You will have to set the RAD_PASSPHRASE for the node to start.
+#   mkdir -p $HOME/.config/systemd/user/
+#   cp radicle-node.service $HOME/.config/systemd/user/radicle-node.service
+#
+# You will have to set the RAD_PASSPHRASE environment variable to the
+# passphrase supplied during `rad auth`, for the node to start, eg.
 #
 #   [Service]
-#   Environment="RAD_PASSPHRASE=[passphrase]"
+#   Environment=RAD_PASSPHRASE=<passphrase>
-
+#
+# Also ensure RAD_HOME is set appropriately.
+#
 [Unit]
 After=syslog.target network.target
 Description=Radicle Node
 
 [Service]
-ExecStart=%h/.radicle/bin/radicle-node
+ExecStart=%h/.radicle/bin/radicle-node --listen 0.0.0.0:8776
+Environment=RAD_HOME=%h/.radicle
 KillMode=process
 Restart=always
 RestartSec=1
 
 [Install]
-WantedBy=multi-user.target
+WantedBy=default.target