add forum formatting to the start of the markup sequence

[sudojunior]

This formatting is exclusive to an initial forum post, and only that message. Removing the leading message requires post to be recreated to format it correctly once more.

# Header 1 ## Header 2 ### Header 3 1. one 2. two 3. three - alpha - bravo - charlie

Header 1 Header 2 Header 3 one two three alpha bravo charlie