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

vintro

2023-08-14 f1c9ca495e450ecb62dade70c4b60d86e106f79c

 quartz/components/styles/darkmode.scss

@@ -2,6 +2,7 @@
  position: relative;
  width: 20px;
  height: 20px;
  margin: 0 10px;

  & > .toggle {
    display: none;