RESOLVE .env error in ./install_powershell.sh

Add note for handling externally managed environment error in Powerline installation

Added an additional note in the README.md under the Powerline installation section.
Provided instructions to modify the install_powerline.sh script to resolve the error caused by the externally managed environment.
Ensured the original README.md content remained unchanged while including necessary troubleshooting steps.

pixegami / terminal-profile