fix: add --user argument when installing addons

[thiswillbeyourgithub]

Signed-off-by: thiswillbeyourgithub [email protected]

pip allows using --user which does the following:

  --user                      Install to the Python user
                              install directory for your
                              platform. Typically
                              ~/.local/, or
                              %APPDATA%\Python on
                              Windows. (See the Python
                              documentation for
                              site.USER_BASE for full
                              details.)

This PR adds the `--user` flag to `llm install`.

This is needed on some install to avoid errors like:
`ERROR: Could not install packages due to an OSError: [Errno 13] Permission denied: '/usr/local/bin/llm'
Consider using the `--user` option or check the permissions.`.