Document CJS/ESM footgun on future common errors page

[nwalters512]

From #1234. Once a page to document common errors exists, document the fact that using Preact in a mixed CJS/ESM Node codebase requires a bundler. Here's the text I had suggested elsewhere:

Preact is not recommended for use in a mixed CJS/ESM codebase running directly in Node without a bundler, as there's a risk that Preact's singletons could be loaded twice. If your first-party code or any dependencies will try to load both the CJS and ESM versions of Preact, you must use a bundler to alias imports of Preact to always resolve to either the CJS or ESM versions.