pnmtorast, pnmtorle, pnmtosgi, pnmtosir, rasttopnm, rletopnm, sgitopnm, sirtopnm: add pages (#11410)

Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>

pages/common/pnmtorast.md

@@ -0,0 +1,12 @@
+# pnmtorast
+
+> Convert a PNM file to a Sun rasterfile.
+> More information: <https://netpbm.sourceforge.net/doc/pnmtorast.html>.
+
+- Convert a PNM image to a RAST image:
+
+`pnmtorast {{path/to/input.pnm}} > {{path/to/output.rast}}`
+
+- Force either `RT_STANDARD` or `RT_BYTE_ENCODED` form for the output:
+
+`pnmtorast -{{standard|rle}} {{path/to/input.pnm}} > {{path/to/output.rast}}`