Add example for Mac OS X background running

etc/macosx-launchd/README.md

@@ -0,0 +1,17 @@
+This directory contains an example for running Syncthing in the
+background under Mac OS X.
+
+ 1. Install the `syncthing` binary in a directory called `bin` in your
+    home directory.
+
+ 2. Edit the `syncthing.plist` file in the two places that refer to your
+    home directory; that is, replace `/Users/jb` with your actual home
+    directory location.
+
+ 3. Copy the `syncthing.plist` file to `~/Library/LaunchAgents`.
+
+ 4. Log out and in again, or run `launchctl load
+    ~/Library/LaunchAgents/syncthing.plist`.
+
+You probably want to turn off "Start Browser" among the settings to
+avoid it opening a browser window on each login.