Consider adding a --mindepth alias for --min-depth

[cstyles]

As of #323, fd supports a --maxdepth alias. However, no such alias exists for --min-depth so the following, seemingly correct command fails:

$ fd --maxdepth=3 --mindepth=2
error: unexpected argument '--mindepth' found

  tip: a similar argument exists: '--min-depth'

Usage: fd --max-depth <depth> --min-depth <depth> [pattern] [path]...

For more information, try '--help'.