docs: note about existing content at same path on different branches

vintro

2023-08-14 f1c9ca495e450ecb62dade70c4b60d86e106f79c

 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;
}