[fboss][docs] Chore: Update BSD License to reflect Meta rebranding

[mustkem]

Description

This pull request updates the BSD License notice in the README to reflect the company’s rebranding from Facebook, Inc. to Meta Platforms, Inc.

Changes made:

• Updated copyright holder:
  • Facebook, Inc. → Meta Platforms, Inc. (formerly Facebook, Inc.)
• Updated attribution clause:
  • Replaced Facebook with Meta in the “Neither the name …” condition.
• Retained original copyright years (2013–2015)
• Preserved full BSD license text for legal continuity.

No functional or code changes are introduced - this is a documentation update for branding and legal accuracy.

Test plan

• ✅ Verify that the updated license text follows BSD-3-Clause format.
• ✅ Confirm that “Meta Platforms, Inc.” is the correct legal entity name.
• ✅ Ensure no other parts of the license text were modified.