Add note about pydantic v1 deprecation

See discussion on #111 (comment)

README.md

@@ -107,6 +107,11 @@ This package currently supports both Pydantic v1 and v2. See the
 [Pydantic migration guide](https://docs.pydantic.dev/2.0/migration/)
 for updating your code.
 
+> [!WARNING]  
+> Pydantic v1 support will be dropped on October 31<sup>st</sup>, 2024,
+> coincident with the [obsolescence of Python 3.8](https://endoflife.date/python).
+> This will be accompanied by the v0.8.0 release of the `curies` package.
+
 ## 👐 Contributing
 
 Contributions, whether filing an issue, making a pull request, or forking, are appreciated. See

src/curies/_pydantic_compat.py

@@ -1,5 +1,7 @@
 """A compatibility layer for pydantic 1 and 2."""
 
+import warnings
+
 from pydantic import __version__ as pydantic_version
 
 __all__ = [
@@ -12,6 +14,15 @@
 
 if PYDANTIC_V1:
     from pydantic import validator as field_validator
+
+    warnings.warn(
+        "The `curies` package will drop Pydantic V1 support on "
+        "October 31st, 2024, coincident with the obsolescence of Python 3.8 "
+        "(see https://endoflife.date/python). This will "
+        "happen with the v0.8.0 release of the `curies` package.",
+        DeprecationWarning,
+        stacklevel=1,
+    )
 else:
     from pydantic import field_validator