docs: add troubleshooting to v2 guide

docs/start/v2.md

@@ -7,6 +7,8 @@ order: 3
 
 All v2 APIs and behaviors are available in v1 with [Future Flags][future-flags]. They can be enabled one at a time to avoid development disruption of your project. After you have enabled all flags, upgrading to v2 should be a non-breaking upgrade.
 
+If you're having trouble see the [Troubleshooting](#troubleshooting) section.
+
 ## `remix dev`
 
 For configuration options, see the [`remix dev` docs][v2-dev-config].
@@ -815,7 +817,7 @@ module.exports = {
 
 ## `serverModuleFormat`
 
-The default server module output format will be changing from `cjs` to `esm`.
+The default server module output format will be changing from `cjs` to `esm`. You can continue to use CJS in v2, many dependencies in your app might not be compatible with ESM.
 
 In your `remix.config.js`, you should specify either `serverModuleFormat: "cjs"` to retain existing behavior, or `serverModuleFormat: "esm"`, to opt into the future behavior.
 
@@ -1077,6 +1079,16 @@ module.exports = {
 };
 ```
 
+## Troubleshooting
+
+### ESM / CommonJS Errors
+
+```
+"SyntaxError: Named export '<something>' not found. The requested module '<something>' is a CommonJS module, which may not support all module.exports as named exports."
+```
+
+Please see the [`serverModuleFormat`](#serverModuleFormat) section.
+
 [future-flags]: ./future-flags
 [remix-config]: ../file-conventions/remix-config
 [flat-routes]: https://github.com/remix-run/remix/discussions/4482