Fix(Crontab): highlight the need for proper crontab setup and CLI execution

[stonebuzz]

This PR improves the documentation of crontab configuration for running GLPI CLI tasks.

Changes

• Emphasizes the need to use the proper web server user (www-data, apache, etc.) when setting up the crontab.
• Provides a more complete crontab example that includes changing the working directory (cd) before running the PHP command.
• Adds guidance on using sudo -u to run CLI tasks manually as the correct user.
• Specifies that the full path to the PHP binary (e.g., /usr/bin/php) may be needed if it's not available in the environment PATH.