macptopbm: add page (#11316)

* macptopbm: add page

---------

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

pages/common/macptopbm.md

@@ -0,0 +1,20 @@
+# macptopbm
+
+> Read a MacPaint file as input and produce a PBM image as output.
+> More information: <https://netpbm.sourceforge.net/doc/macptopbm.html>.
+
+- Convert a MacPaint file into a PGM image:
+
+`macptopbm {{path/to/file.mac}}`
+
+- Skip over a specified number of bytes when reading the file:
+
+`macptopbm -extraskip {{N}}`
+
+- Suppress all informational messages:
+
+`macptopbm -quiet`
+
+- Display version:
+
+`macptopbm -version`