Update README according to latest 'MAIL' header changes

README.md

@@ -20,7 +20,7 @@ The `POST` method is used to add a log to the database.
 * The second line of the input is the type (se below).
 * The third one is the date.
 * The fourth one is a list of comma separated tags.
-* The fifth one is "Yes" if the server should email the log contents after storing them in the database (the mail program should be preconfigured for this to work)
+* The fifth one is, optionally, "MAIL" if the server should email the log contents after storing them in the database (the mail program should be preconfigured for this to work)
 * The remainder of the file (until EOF is met) is the content of the log.
 
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