Update cheatsheets

ppmtv

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# ppmtv
+
+> Make a PPM Image look like taken from an American TV.
+> Dim every other row of image data down by the specified dim factor (a number between 0 and 1).
+> More information: <https://netpbm.sourceforge.net/doc/ppmtv.html>.
+
+- Give the PPM image an American TV appearance:
+
+`ppmtv {{dim_factor}} {{path/to/file.ppm}} > {{path/to/output.ppm}}`
+
+- Suppress all informational messages:
+
+`ppmtv -quiet`
+
+- Display version:
+
+`ppmtv -version`