pgmcrater, pamcrater, pamshadedrelief: add pages (#12401)

pages/common/pamshadedrelief.md

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+# pamshadedrelief
+
+> Generate a shaded relief from an elevation map.
+> See also: `pamcrater`, `ppmrelief`.
+> More information: <https://netpbm.sourceforge.net/doc/pamshadedrelief.html>.
+
+- Generate a shaded relief image with the input image interpreted as an elevation map:
+
+`pamshadedrelief < {{path/to/input.pam}} > {{path/to/output.pam}}`
+
+- Gamma adjust the image by the specified factor:
+
+`pamshadedrelief -gamma {{factor}} < {{path/to/input.pam}} > {{path/to/output.pam}}`