pnmtopng: add page (#11072)

* pnmtopng: add page

* Update pnmtopng.md

* Updated syntax

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

---------

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

pages/common/pnmtopng.md

@@ -0,0 +1,12 @@
+# pnmtopng
+
+> Converts a PNM image file to PNG image format.
+> More information: <https://netpbm.sourceforge.net/doc/pnmtopng.html>.
+
+- Read a PNM image as input and produce a PNG image as output:
+
+`pnmtopng {{path/to/file.pnm}} > {{path/to/file.png}}`
+
+- Display version:
+
+`pnmtopng -version`