Missing docs on code splitting

[dalechyn]

Docs currently say nothing about how frog code can be split, yet code splitting is leveraged in the internal playground.

frog/playground/src/index.tsx

Lines 180 to 187 in 21dff58

	.route('/ui', uiSystemApp)
	.route('/fonts', fontsApp)
	.route('/middleware', middlewareApp)
	.route('/neynar', neynarApp)
	.route('/routing', routingApp)
	.route('/transaction', transactionApp)
	.route('/todos', todoApp)
	.frame('/:dynamic', (c) => {

That needs to be documented properly as I've seen many frames implementing unoptimal code-splitting, sometimes even breaking the build (#30), and which can unintentionally cause cyclic dependency issues.

Other refs: https://discord.com/channels/1156791276818157609/1212219334370529370/1225708808484032562