sdef, xml2man: add page (#7927)

pages/osx/xml2man.md

@@ -0,0 +1,16 @@
+# xml2man
+
+> Compile MPGL to mdoc.
+> More information: <https://developer.apple.com/library/archive/documentation/DeveloperTools/Conceptual/HeaderDoc/mpgl/mpgl.html>.
+
+- Compile an MPGL file to a viewable man page:
+
+`xml2man {{path/to/command.mxml}}`
+
+- Compile an MPGL file to a specific output file:
+
+`xml2man {{path/to/service.mxml}} {{path/to/service.7}}`
+
+- Compile an MPGL file to a specific output file, overwriting if it already exists:
+
+`xml2man -f {{path/to/function.mxml}} {{path/to/function.3}}`