zeisstopnm: add page (#10888)

* zeisstopnm: add page

---------

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

pages/common/zeisstopnm.md

@@ -0,0 +1,12 @@
+# zeisstopnm
+
+> Convert a Zeiss confocal file to Netbpm format.
+> More information: <https://manned.org/zeisstopnm.1>.
+
+- Convert a Zeiss cofocal file into either `.pgm` or `.ppm` format:
+
+`zeisstopnm {{path/to/file}}`
+
+- Convert a Zeiss cofocal file to Netbpm format while explicitly specifying the target file type:
+
+`zeisstopnm -{{pgm|ppm}} {{path/to/file}}`