chore: document legacy version

Author: b-long

docs/LEGACY_VERSION.md

@@ -0,0 +1,20 @@
+# Legacy Version
+
+The legacy version of this project is available for now using the Github branch: `0.2.x`. 
+
+You can access it directly via the following link: 
+https://github.com/b-long/opentdf-python-sdk/tree/0.2.x
+
+In extreme cases, if you need to use this legacy version, please refer to the information
+available in that branch. However, it is highly recommended to use the latest version of the project for better performance, security, and support.
+
+## About the legacy version
+
+The legacy version was built using [gopy](https://github.com/go-python/gopy), to create an initial
+release of the OpenTDF Python SDK. It provided basic functionalities for interacting with the OpenTDF platform, including data encryption and decryption.
+
+## PyPI
+
+The most recent release of the legacy version is available on PyPI and can 
+be found at the following link:
+https://pypi.org/project/otdf-python/0.2.20/