doc/Makefile: Don't show Makefile comments in output
The comments makes sense when editing Makefile, but not when watching its
output where it looks too much like error messages.
% replace file with dir
initializing destination source-hg repository
scanning source...
sorting...
converting...
2 add d file
1 replace with d dir
0 add d/a
% manifest of tip
644 d/a
1 files updated, 0 files merged, 0 files removed, 0 files unresolved