Later: write proper README.

How can it be possible that there has been README file reading
"Insert a description of your plugin here, with any notes, etc. about using it" for eight years?

plugins/Later/README.md

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+Later - leave small messages to users
+
+# Later
+
+Later allows you to leave small notes to people. The messages are delivered next time when the user is seen by the bot.
+
+# How to use it?
+
+Use the "later tell" command to leave a message to a user. If you sent the message by accident or want to cancel it, you can use the "later undo" command to remove the latest later, which you have sent.
+
+You can also see the people who have notes waiting for them by using the "later notes" command. If you specify a nickname in "later notes" command, you will see the notes, which are waiting for the nickname.
+
+# Privacy
+
+As you probably noticed from above, this plugin isn't private. Everyone can see notes sent by anyone as the "plugin help later" says:
+
+```
+Used to do things later; currently, it only allows the sending of nick-based notes. Do note (haha!) that these notes are *not* private and don't even pretend to be; if you want such features, consider using the Note plugin.
+```
+
+The Note plugin identifies people by username instead of nickname and allows only users to send notes. The only people who are able to read notes are the sender, receiver and the owner.

plugins/Later/README.txt

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-Insert a description of your plugin here, with any notes, etc. about using it.