Comments prepended with `##` appear in the output of `make commands`.
This commit changes `#` to `##` in front of `lesson-check` so that it
appears in the output of `make commands`.
_episodes/%.md: _episodes_rmd/%.Rmd
@bin/knit_lessons.sh $< $@
-# * lesson-check : validate lesson Markdown
+## * lesson-check : validate lesson Markdown
lesson-check : lesson-fixme
@${PYTHON} bin/lesson_check.py -s . -p ${PARSER} -r _includes/links.md