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

vintro

2023-08-14 f1c9ca495e450ecb62dade70c4b60d86e106f79c

 quartz/styles/callouts.scss

@@ -7,6 +7,7 @@
  padding: 0 1rem;
  overflow-y: hidden;
  transition: max-height 0.3s ease;
  box-sizing: border-box;

  & > *:nth-child(2) {
    margin-top: 0;