Add system-info macOS user agent

The `system-info` directory contains scripts and configuration files to
install and remove a `launchd` user agent on macOS which collects
information about the system and outputs it to the file
`~/.cache/tmux/system-info`. This file is then read periodically by
`tmux` and the contents displayed in the status line.

system-info/system-info.plist

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+  <dict>
+    <key>Label</key>
+    <string>system-info</string>
+    <key>ProgramArguments</key>
+    <array>
+      <string>/Users/benie/.config/tmux/system-info/system-info-macOS.sh</string>
+    </array>
+    <key>KeepAlive</key>
+    <true/>
+  </dict>
+</plist>