Update cheatsheets

ppmspread

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# ppmspread
+
+> Displace the pixels in a PPM image by a randomized amount.
+> More information: <https://netpbm.sourceforge.net/doc/ppmspread.html>.
+
+- Displace the pixels in a PPM image by a randomized amount that is at most a:
+
+`ppmspread {{a}} {{path/to/input_file.ppm}} > {{path/to/output_file.ppm}}`
+
+- Specify a seed to a the pseudo-random number generator:
+
+`ppmspread {{a}} {{path/to/input_file.ppm}} -randomseed {{seed}} > {{path/to/output_file.ppm}}`