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

vintro

2023-08-14 f1c9ca495e450ecb62dade70c4b60d86e106f79c

 quartz/styles/variables.scss

@@ -1,5 +1,6 @@
$pageWidth: 800px;
$pageWidth: 750px;
$mobileBreakpoint: 600px;
$tabletBreakpoint: 1200px;
$sidePanelWidth: 400px;
$topSpacing: 6rem;
$fullPageWidth: $pageWidth + 2 * $sidePanelWidth;