Please check if the PR fulfills these requirements
[ ] The commit message follows our guidelines
[ ] Tests for the changes have been added (for bug fixes / features)
[ ] Docs have been added / updated (for bug fixes / features)
What kind of change does this PR introduce?
Doc website update
What is the current behavior?
The PowSyBl logo links to powsybl.org
What is the new behavior (if this is a feature change)?
Now it links to the new parent website https://powsybl.readthedocs.io, allowing a better navigation between powsybl projects
Does this PR introduce a breaking change or deprecate an API?
Please check if the PR fulfills these requirements
What kind of change does this PR introduce?
Doc website update
What is the current behavior?
The PowSyBl logo links to powsybl.org
What is the new behavior (if this is a feature change)? Now it links to the new parent website https://powsybl.readthedocs.io, allowing a better navigation between powsybl projects
Does this PR introduce a breaking change or deprecate an API?