Clarify -teenth

Foreign-language peeps shouldn't go chasing down the rabbit hole
of asking translators about the word.

Author: kytrinyx

meetup.md

@@ -7,6 +7,8 @@ Examples are
 - the Wednesteenth
 - the last Thursday
 
-There are exactly 7 days that end in '-teenth'. Therefore, one is
-guaranteed that each day of the week will have a '-teenth' in every
-month.
+Note that "Monteenth", "Tuesteenth", etc are all made up words. There
+was a meetup whose members realised that there are exactly 7 days that
+end in '-teenth'. Therefore, one is guaranteed that each day of the week
+(Monday, Tuesday, ...) will have exactly one date that is named with '-teenth'
+in every month.