docs: fix typo now → not

docs/USER_NAMES.md

@@ -26,7 +26,7 @@ Generally, the same rules apply for user as for group names.
   is defined as [lower and upper case ASCII letters, digits, period,
   underscore, and
   hyphen](https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_282),
-  with the restriction that hyphen is now allowed as first character of the
+  with the restriction that hyphen is not allowed as first character of the
   user name. Interestingly no size limit is declared, i.e. in neither
   direction, meaning that strictly speaking according to POSIX both the empty
   string is a valid user name as well as a string of gigabytes in length.