Couple spelling errors on your docs home page

Just wanted to point out a couple spelling mistakes on the docs home page.

organisation should be organization.

explanitory should be explanatory

writeup would look better as write-up

Hey @geeked,

welcome to the forum and thanks for pointing those typos out.

I opened a PR with your suggested changes.

If you happen to find anymore typo in the future, please open an issue in the hedgedoc repo.