Update README

README.md

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 # openttd-admin
-Golang interface to an OpenTTD server
+
+Golang interface to an OpenTTD server, and standalone 'openttd_multitool' binary 
+for simple, periodic server operations.
+
+The latter might include periodically:
+
+* sending messages to connected players
+* saving the game to a custom, datestamped save
+* generating datestamped screenshots
+
+## openttd_multitool
+
+The openttd_multitool connects to the OpenTTD Admin port (default 3977) 
+and stays connected. It monitors the game date, and performs your custom commands
+at periodic intervals.
+
+Possible intervals are:
+
+* daily
+* monthly
+* yearly
+
+These intervals are obviously in game time!
+
+You can configure the tool to send any command that you would type at the OpenTTD
+console. Here are a few examples:
+
+    openttd_multitool --hostname localhost --password abc --daily "say \"Hello to all players\""
+
+This sends an annoying message to all players, every day. Note the quoting requirements to ensure
+that the argument to the "say" command in OpenTTD comes through as a single argument.
+
+    openttd_multitool --hostname localhost --password abc --monthly "save mygame-%Y-%M"
+
+This saves the game once per month, with a filename like "mygame-2020-11.sav".
+
+    openttd_multitool --hostname localhost --password abc --yearly "screenshot giant screenshot-%Y%M%D"
+
+This generates a screenshot once per year of the entire map, with a name like "screenshot-20201121.png".
+
+NOTE that your OpenTTD server needs to support generating screenshots (some dedicated servers compiled without
+graphics will not work) and the appropriate graphics packs need to also be installed. 
+
+Additionally, when using the "screenshot giant" command, the entire server will freeze for that time, almost
+certainly kicking off all clients, unless your map is very small or your server is very very fast! 
+
+No harm is done in that case, they can just reconnect after the screenshot is finished.
+