feat: additional --preview-interval values (#1915)

Co-authored-by: leejet <leejet714@gmail.com>

examples/cli/main.cpp

@@ -94,7 +94,7 @@ struct SDCliParams {
         options.int_options = {
             {"",
              "--preview-interval",
-             "interval in denoising steps between consecutive updates of the image preview file (default is 1, meaning updating at every step)",
+             "preview interval: in each sampling pass, positive N updates every Nth denoiser step and -N previews only completed logical step N; 0 previews the final completed step of the first pass (base-resolution or high-noise). Default: 1",
              &preview_interval},
             {"",
              "--output-begin-idx",