Update README.md for version 1.2.0

[castrokelly]

This pull request updates the README.md file to reflect the changes and improvements introduced in version 1.2.0 of the 3W Toolkit.

Key changes:

• Added a new section for version 1.2.0, describing the key changes made to adapt the toolkit to the 3W Dataset 2.0.
• Highlighted the modifications in each sub-module (base.py, dev.py, misc.py, and __init__.py).
• Updated the release date for version 1.2.0.

This update ensures that the README.md file provides accurate and up-to-date information about the 3W Toolkit and its compatibility with the 3W Dataset 2.0.

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