fixing markdown in front of 'background'

The hashtags in front of 'background' are showing up as hashtags and not working as a header on the website, but they're working fine in preview. Hoping this fixes it.
fixing "improve this content" instructions

Since we still have that prose bug that allows unauthenticated users to make changes and then loses them (https://github.com/prose/prose/issues/643), I've added a step encouraging people to authenticate first.
Merge pull request #255 from leahbannon/small-edits

fixing markdown in front of 'background'