Update pmtiles upload --help

[zstadler]

Related to #194

[bdon]

the help text now looks like this:

upload --bucket=STRING <input-pm-tiles> <remote-pm-tiles>
    Upload a local archive to remote storage.

Is there a way to make it <input-pmtiles> instead of input-pm-tiles?

[zstadler]

go-pmtiles --help now shows

  upload --bucket=STRING <input-pmtiles> <remote-pmtiles>
    Upload a local archive to remote storage.

and go-pmtiles upload --help shows

Usage: go-pmtiles upload --bucket=STRING <input-pmtiles> <remote-pmtiles>

Upload a local archive to remote storage.

Arguments:
  <input-pmtiles>     The local PMTiles file
  <remote-pmtiles>    The name for the remote PMTiles source

Flags:
  -h, --help                 Show context-sensitive help.

      --max-concurrency=2    # of upload threads
      --bucket=STRING        Bucket to upload to.