Fix typo in xml_tools TODO and update CONTRIBUTING.md

[greninja]

Low-hanging PR to start contributing to this project.

Key Changes

• Fix typo in TODO comment in rigging/transform/xml_tools.py (cased → cases).
• Update CONTRIBUTING.md: remove the CLA step from the PR guidelines and the Facebook CLA section. Not sure but I was reading the contributing guidelines and this section seemed a bit off -- since it refers to Facebook’s CLA and this repo is clearly not one, so it doesn’t seem to apply here -- removed for now; maintainers can add a dreadnode-specific CLA link if needed. Apologies if I misunderstood it.

Added

• (none)

Changed

• rigging/transform/xml_tools.py: TODO comment now reads “handle cases where…”.
• .github/CONTRIBUTING.md: Removed the Contributor License Agreement bullet from the PR guidelines and the Facebook CLA section.

Removed

• References to Facebook and the code.facebook.com CLA from CONTRIBUTING.md.