pamoil, pgmbentley, pgmdeshadow, pgmoil, ppmrainbow, ppmrelief, ppmshadow, ppmshift, ppmspread, ppmtoacad, ppmtobmp, ppmtoicr: add pages (#11433)

pages/common/ppmrainbow.md

@@ -0,0 +1,16 @@
+# ppmrainbow
+
+> Generate a rainbow.
+> More information: <https://netpbm.sourceforge.net/doc/ppmrainbow.html>.
+
+- Generate a rainbow consisting of the specified colors:
+
+`ppmrainbow {{color1 color2 ...}} > {{path/to/output_file.ppm}}`
+
+- Specify the size of the output in pixels:
+
+`ppmrainbow -width {{width}} -height {{height}} {{color1 color2 ...}} > {{path/to/output_file.ppm}}`
+
+- End the rainbow with the last color specified, do not repeat the first color:
+
+`ppmrainbow -norepeat {{color1 color2 ...}} > {{path/to/output_file.ppm}}`