Add request for Markdown to the Success Stories submission form

[loren-c]

Success Stories are easiest for me to work with when they are submitted in Markdown. Currently, the submission form doesn't request Markdown (or indicate that Markdown is acceptable.)

On https://www.python.org/success-stories/create/, I'd like to add a note at the "Content" text submission box that says something like "Markdown formated text is strongly preferred"

Thank you!