docs: fix typo in `authoring content.md` (#408)

Ben Schlegel

2023-08-24 9d2340e90b55fb9480e0901bc7360f3d72e688da

 quartz/components/Header.tsx

@@ -9,7 +9,7 @@
  display: flex;
  flex-direction: row;
  align-items: center;
  margin: 2em 0;
  margin: 2rem 0;
  gap: 1.5rem;
}