Improve discoverability of message to set $PATH on Windows

Summary

A number of users are running into trouble installing Streamlit on Windows because they don’t realize they have to manually edit their $PATH.

• https://github.com/streamlit/streamlit/issues/1252
• https://discuss.streamlit.io/t/getting-an-error-streamlit-is-not-recognized-as-an-internal-or-external-command-operable-program-or-batch-file/361/10
• https://stackoverflow.com/questions/60866205/python-streamlit-run-issue

Solution 1

Set the $PATH automatically after installation on Windows.

Solution 2

If Solution 1 is impossible for some reason, then we could increase the discoverability of the message to set the $PATH on Windows, following this suggestion.

Ways to make it stand out:

1. Make sure this message is at the bottom of the installation messages, as much as possible.
2. Use console colors (is this possible on Windows?)
3. Use capital letters. (If #2 doesn’t work.)
4. Separate this message from others with a newline above and below.

We don’t need to do all of these options, but it’d be nice to have the minimum to improve discoverability.

[nthmost]

If we want Streamlit to add to the $PATH itself, this might have a solution:

https://stackoverflow.com/questions/1085852/interface-for-modifying-windows-environment-variables-from-python

I personally (as someone who isn’t anywhere near an expert on Windows programming) don’t feel comfortable integrating something like this as a solution. Which is why I’m advocating for a documentation based approach instead.

[randyzwitch]

Without directly modifying the Windows $PATH variable directly, there are two approaches we should consider here:

I agree that we shouldn’t modify the PATH, that feels too intrusive.

We already have the wiki content in the docs here, but it’s under ‘Troubleshooting’. It probably should be front and center in a ‘getting started’ section, and maybe the exact error message text could be part of the ‘Troubleshooting’ section.