pnmtojpeg: add page (#11081)

Co-authored-by: Juri Dispan <juri.dispan@posteo.net>

pages/common/pnmtojpeg.md

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+# pnmtojpeg
+
+> Converts a PNM image file to the JPEG/JFIF/EXIF image format.
+> More information: <https://netpbm.sourceforge.net/doc/pnmtojpeg.html>.
+
+- Read a PNM image as input and produce a JPEG/JFIF/EXIF image as output:
+
+`pnmtojpeg {{path/to/file.pnm}} > {{path/to/file.jpg}}`
+
+- Display version:
+
+`pnmtojpeg -version`