Make "cpupower" building process more user friendly by adding 'help'
target to the main makefile. This target describes various build
and cleaning options available to the user.
Signed-off-by: Roman Storozhenko <romeusmeister@xxxxxxxxx>
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V1 -> V2:
- Enchanced patch description
- Reformat patch
- Link v1: https://lore.kernel.org/linux-pm/20240614-make-help-v1-1-513118646b71@xxxxxxxxx/
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