docs(lambda-python): add troubleshooting for Finch (#24646)

Add troubleshooting instructions to resolve a weird error produced by Finch.

Fixes #24458.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: rix0rrr

packages/@aws-cdk/aws-lambda-python/README.md

@@ -285,3 +285,24 @@ new python.PythonFunction(this, 'function', {
   },
 });
 ```
+
+## Troubleshooting
+
+### Containerfile: no such file or directory
+
+If you are on a Mac, using [Finch](https://github.com/runfinch/finch) instead of Docker, and see an error
+like this:
+
+```txt
+lstat /private/var/folders/zx/d5wln9n10sn0tcj1v9798f1c0000gr/T/jsii-kernel-9VYgrO/node_modules/@aws-cdk/aws-lambda-python-alpha/lib/Containerfile: no such file or directory
+```
+
+That is a sign that your temporary directory has not been mapped into the Finch VM. Add the following to `~/.finch/finch.yaml`:
+
+```yaml
+additional_directories:
+  - path: /private/var/folders/
+  - path: /var/folders/
+```
+
+Then restart the Finch VM by running `finch vm stop && finch vm start`.