Update cheatsheets

ppmtoppm

@@ -0,0 +1,17 @@
+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# ppmtoppm
+
+> Copy a PPM image.
+> More information: <https://netpbm.sourceforge.net/doc/ppmtoppm.html>.
+
+- Copy a PPM image (i.e. a PBM, PGM or PPM image) from `stdin` to `stdout`:
+
+`ppmtoppm < {{path/to/image.ppm}} > {{path/to/output.ppm}}`
+
+- Display version:
+
+`ppmtoppm -version`