pamcomp, pnmcomp, pnmconvol, pnmcrop, pnmgamma: add pages (#12197)

* pamcomp, pnmcomp, pnmconvol, pnmcrop, pnmgamma: add pages

* Update pages/common/pnmgamma.md

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

---------

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

pages/common/pnmconvol.md

@@ -0,0 +1,20 @@
+# pnmconvol
+
+> Convolute a PNM image.
+> More information: <https://netpbm.sourceforge.net/doc/pnmconvol.html>.
+
+- Convolve a PNM image with the specified convolution matrix:
+
+`pnmconvol -matrix=-1,3,-1 {{path/to/image.pnm}} > {{path/to/output.pnm}}`
+
+- Convolve a PNM image with the convolution matrix in the specified files, one for each layer in the input image:
+
+`pnmconvol -matrixfile {{path/to/matrix1,path/to/matrix2,...}} {{path/to/image.pnm}} > {{path/to/output.pnm}}`
+
+- Convolve a PNM image with the convolution matrix in the specified PNM file:
+
+`pnmconvol {{path/to/matrix.pnm}} {{path/to/image.pnm}} > {{path/to/output.pnm}}`
+
+- Normalize the weights in the convolution matrix such that they add up to one:
+
+`pnmconvol -matrix=-1,3,-1 -normalize {{path/to/image.pnm}} > {{path/to/output.pnm}}`