docs: document `setChokidarConfig` method

[murtuzaalisurti]

• Recently came across a scenario where the auto reload feature (watch files) of 11ty wasn't working in a docker container for mounted files.
• You can find the reason here https://syntackle.com/blog/containerizing-a-nextjs-application-using-docker-st_G0u/#live-reloading-hmr.
• Chokidar provides the feature of polling — which you can set in chokidar watch options.
• 11ty does provide a user config method named setChokidarConfig to set the chokidar watch options, but I didn't find it documented — instead found it through mastodon.