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

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

pages/common/rletopnm.md

@@ -0,0 +1,16 @@
+# rletopnm
+
+> Convert a Utah Raster Tools RLE image file to a PNM file.
+> More information: <https://netpbm.sourceforge.net/doc/rletopnm.html>.
+
+- Convert an RLE image to a PNM file:
+
+`rletopnm {{path/to/input.rle}} > {{path/to/output.pnm}}`
+
+- Create a PGM image containing the RLE file's alpha channel:
+
+`rletopnm -alphaout {{path/to/alpha_file.pgm}} {{path/to/input.rle}} > {{path/to/output.pnm}}`
+
+- Operate in verbose mode and print the contents of the RLE header to `stdout`:
+
+`rletopnm -verbose {{path/to/input.rle}} > {{path/to/output.pnm}}`