also introduces the utils folder

… on every update

…c#672)

* Add load from user config from in XDG_CONFIG_HOME if available

This update introduces the flexibility to load the configuration file from
multiple locations, prioritizing user preferences and system standards.
Previously, the configuration was strictly read from a hardcoded
system path (`/etc/auto-cpufreq.conf`). Now, the application first checks if the
user has specified a configuration file path via command line arguments. If not,
it looks for a configuration file in the user's config
directory (`$XDG_CONFIG_HOME/auto-cpufreq/auto-cpufreq.conf`). If neither is
found, it defaults to the original system-wide configuration file.

This allows users to add their auto-cpufreq configuration to their dotfiles.

* If --config is set but invalid, exit with error

* Remove redundant empty string check on config file path

* Remove duplicate isfile check for config path

See also: AdnanHodzic#672 (comment)

* Update configuration options in README

See also: AdnanHodzic#672

Co-authored-by: Steven Braun <steven.braun.mz@gmail.com>