Update README.md

Description of the library
Update README.md
Update README.md
Update README.md
initialisation of the project file structure
initialisation of the project file structure
initialisation of the project file structure (2)
initialisation of the project file structure (3)
First clock implementation + messages definition
improve the Clock and the code, better separates the components
add tests for the clock component
write some tests for basis components
add licence headers
Merge branch 'feature/clock-rewriting' of https://github.com/Spirals-Team/powerapi into feature/clock-rewriting
rebase on the develop branch, add dependency in README