picttoppm, pnmtops, ppmtopict, ppmtopuzz, ppmtosixel, psidtopgm, pstopnm, qrttoppm: add pages (#11413)

pages/common/pstopnm.md

@@ -0,0 +1,16 @@
+# pstopnm
+
+> Convert a PostScript file to a PNM image.
+> More information: <https://netpbm.sourceforge.net/doc/pstopnm.html>.
+
+- Convert a PS file to PNM images, storing page N of the input to `path/to/fileN.ppm`:
+
+`pstopnm {{path/to/file.ps}}`
+
+- Explicitly specify the output format:
+
+`pstopnm -{{pbm|pgm|ppm}} {{path/to/file.ps}}`
+
+- Specify the resolution of the output in dots per inch:
+
+`pstopnm -dpi {{n}} {{path/to/file.ps}}`