message: scripts: update docs for 'generate-unicode-tables'
  The docs are now updated to work with Unicode 14. (In particular,
  emoji-data.txt no longer needs to be downloaded separately.) We also
  include a note about adding a new case for "age" in regex-syntax.
diff: #
  # $ mkdir ucd
  # $ cd ucd
  -# $ curl -LO https://www.unicode.org/Public/zipped/12.1.0/UCD.zip
  +# $ curl -LO https://www.unicode.org/Public/zipped/14.0.0/UCD.zip
  # $ unzip UCD.zip
  -# $ curl -LO https://unicode.org/Public/emoji/12.0/emoji-data.txt
  #
  # And then run this script from the root of this repository by pointing it at
  # the data directory downloaded above:
  #
  # $ ./scripts/generate-unicode-tables path/to/ucd
  +#
  +# Once complete, if you are upgrading to a new version of Unicode,
  +# you'll need to add a new "age" value to the 'ages' routine in
  +# regex-syntax/src/unicode.rs.
  if [ $# != 1 ]; then
  echo "Usage: $(basename "$0") <ucd-data-directory>" >&2
  