@agusputra I agree with your suggestion about helper buttons. The open source project Rocket Chat has an unobtrusive way of hinting basic Markdown syntax.
0_1447403857660_markdown_hint1.png
Simply a line of greyed text that becomes regular text on mouseover
0_1447403978825_markdown_hint2.png
It might be useful to have something like this at the bottom of the editor input field.