Add solution to mixed local and non-local install to troubleshooting guide

[TimMonko]

However, I think the suggestion to remove napari from site-packages is not going to be the easiest thing for many people running into this error. Indeed, I think I might know how to do that, but confidence would be low. Perhaps it would be easiest to link to a section in the docs Troubleshooting page. The instructions could be a bit more, and even say, 'if you're unsure about this, we recommend creating a new environment'.

@Czaki would you be able to do that? We can add the link directly to the error message

Originally posted by @TimMonko in napari/napari#7745 (comment)

After, we follow-up with a PR to napari/napari linking the troubleshooting page to the error introduced in napari/napari#7745

From that PR description:

Description

Check if there is a mix of local and non-local installation of napari and then stop process.

Works only if run napari as module python -m napari not when start napari from script.

$ napari                                                                                                                              
Traceback (most recent call last):
  File "/home/czaki/.pyenv/versions/napari_3.12/bin/napari", line 5, in <module>
    from napari.__main__ import main
  File "/home/czaki/Projekty/napari/src/napari/__init__.py", line 52, in <module>
    _check_installation_path()
  File "/home/czaki/Projekty/napari/src/napari/__init__.py", line 49, in _check_installation_path
    raise RuntimeError(text)
RuntimeError: Mix of local and non local installation detected.
Napari is installed in editable mode but also found napari directory in site-packages.
Path to a napari directory: /home/czaki/.pyenv/versions/3.12.9/envs/napari_3.12/lib/python3.12/site-packages/napari.
Mix of local and non local installation is leading to hard to understand errors. Please remove the napari directory from site-packages