docs: add explorer example for advanced `sortFn` (#564)

Sidney

2023-12-28 e1b6a0014cabf07ddc7e7931912aece471959224

 quartz/processors/filter.ts

@@ -1,5 +1,5 @@
import { BuildCtx } from "../ctx"
import { PerfTimer } from "../perf"
import { BuildCtx } from "../util/ctx"
import { PerfTimer } from "../util/perf"
import { ProcessedContent } from "../plugins/vfile"

export function filterContent(ctx: BuildCtx, content: ProcessedContent[]): ProcessedContent[] {