Addressing PATH caveats

Is your feature request related to a problem? Please describe.

I tried installing chezmoi on a fresh Ubuntu Studio installation today and became extremely frustrated with the documented installation procedure failed. Specifically, the fact that the curl | sh installation installs to ./bin, which is not in the PATH environment variable by default.

This has been filed before in #2064, #2993, and #3689. However, I don't propose changing the user's PATH.

Describe the solution you'd like

I recommend a two-pronged approach:

1. Detect when the chezmoi has been installed in a directory that doesn't exist in PATH, then print a message to the user identifying the actual installed path and recommend that they add it to their PATH var. Something like:

Installed chezmoi into /home/example/bin/.
This directory is not in your current PATH.
You can run it now using "/home/example/bin/chezmoi".
See [documentation link] to make it available as "chezmoi".

This way, there's no need to automatically edit the user's shell configuration, as #2993 proposed.

1. As part of that [documentation link] above, explain in the installation guide that the installer does not update PATH and offer instructions on how to do so so the user can invoke "chezmoi" from anywhere.

Please let me know if you'd like me to open a PR with these minor additions.

Describe alternatives you've considered

Alternative: Not doing anything. Most seasoned Linux veterans will know how to get around the incomplete documentation, but new users who are still learning Linux will get frustrated that chezmoi doesn't work out of the box even while following the instructions to the letter.

Given that this has been an ongoing problem for over four years now, I think the above mentioned steps are minor enough to be incorporated if it means helping out new users.

Additional context

See above for the links to previous reports about this issue, which should be more than enough additional context.