Docs for deno.json don't mention minimumDependencyAge setting

In light of the recent axios supply chain attack, the `deno install --minimum-dependency-age` flag and the deno.json `minimumDependencyAge` setting are very important, but [the docs page for deno.json](https://docs.deno.com/runtime/fundamentals/configuration/) doesn't mention the `minimumDependencyAge` setting yet.