docs: clarify git only sets modified

quartz.config.ts

@@ -47,7 +47,9 @@ const config: QuartzConfig = {
       Plugin.FrontMatter(),
       Plugin.TableOfContents(),
       Plugin.CreatedModifiedDate({
-        priority: ["frontmatter", "filesystem"], // you can add 'git' here for last modified from Git but this makes the build slower
+        // you can add 'git' here for last modified from Git
+        // if you do rely on git for dates, ensure defaultDateType is 'modified'
+        priority: ["frontmatter", "filesystem"],
       }),
       Plugin.Latex({ renderEngine: "katex" }),
       Plugin.SyntaxHighlighting(),