uniq: move help strings to markdown file

[miles170]

#4368

$ cargo run -- uniq --help
    Finished dev [unoptimized + debuginfo] target(s) in 0.14s
     Running `target/debug/coreutils uniq --help`
Report or omit repeated lines.

Usage: target/debug/coreutils uniq [OPTION]... [INPUT [OUTPUT]]...

Arguments:
  [files]...

Options:
  -D, --all-repeated[=<delimit-method>]  print all duplicate lines. Delimiting is done with blank lines. [default: none] [possible values: none, prepend, separate]
      --group[=<group-method>]           show all items, separating groups with an empty line. [default: separate] [possible values: separate, prepend, append, both]
  -w, --check-chars <N>                  compare no more than N characters in lines
  -c, --count                            prefix lines by the number of occurrences
  -i, --ignore-case                      ignore differences in case when comparing
  -d, --repeated                         only print duplicate lines
  -s, --skip-chars <N>                   avoid comparing the first N characters
  -f, --skip-fields <N>                  avoid comparing the first N fields
  -u, --unique                           only print unique lines
  -z, --zero-terminated                  end lines with 0 byte, not newline
  -h, --help                             Print help
  -V, --version                          Print version

Filter adjacent matching lines from INPUT (or standard input),
writing to OUTPUT (or standard output).

Note: 'uniq' does not detect repeated lines unless they are adjacent.
You may want to sort the input first, or use 'sort -u' without 'uniq'.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/tail-2/inotify-dir-recreate. tests/tail-2/inotify-dir-recreate is passing on 'main'. Maybe you have to rebase?

[cakebaker]

Thanks!