add similarity levels to --help

[tincanfury]

Similar to the delete methods, adding the level options to similarity-preset to help output would be, helpful
current --help output,

          Methods to choose similarity level of images which will be considered as duplicated.

          [default: High]```
copied from the code,
"minimal"
"verysmall"
"small"
"medium"
"high"
"veryhigh"
"original"