add note about tweeted in 2019/mills

2019/mills/README.md

@@ -46,6 +46,14 @@ guidelines for the IOCCC?
 
 You decide. :-)
 
+**Historic note**: The award title use of the word "**tweeted**"
+should be regarded as a IOCCC anachronism.  Over the years the
+maximum size of a _tweet_ changed since this entry won the IOCCC.
+Moreover, the [IOCCC now uses Mastodon](../../faq.html#try_mastodon)
+instead of whatever someone (and especially those who appear to
+have poor impulse control) chooses to call the platform where people
+used to tweet.
+
 
 ## Author's remarks: