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.
#!/bin/sh
echo "[extensions]" >> $HGRCPATH
echo "hgk=" >> $HGRCPATH
hg init repo
cd repo
echo a > a
hg ci -Am adda
hg debug-cat-file commit 0