Update PSC.md to add Julien Radoux as a PSC member

Summary

This MR adds Julien Radoux as an official PSC member.

See nomination here: https://forum.orfeo-toolbox.org/t/nomination-of-julien-radoux-as-psc-member/264/5

Copyright

The copyright owner is CNES and has signed the ORFEO ToolBox Contributor License Agreement.

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Check before merging:

• All discussions are resolved
• At least 2 votes from core developers, no vote.
• The feature branch is (reasonably) up-to-date with the base branch
• Dashboard is green
• Copyright owner has signed the ORFEO ToolBox Contributor License Agreement
• Optionally, run git diff develop... -U0 --no-color | clang-format-diff.py -p1 -i on latest changes and commit

added patch label

merged

mentioned in commit 01260cbb

changed milestone to %7.0.0

added documentation label