docs: add cuda-core FT docs

Author: cpcloud

cuda_core/docs/source/install.rst

@@ -42,6 +42,18 @@ and likewise use ``[cu13]`` for CUDA 13.
 Note that using ``cuda.core`` with NVRTC installed from PyPI via ``pip install`` requires
 ``cuda.bindings`` 12.8.0+. Likewise, with nvJitLink it requires 12.8.0+.
 
+Free-threading Build Support
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+As of cuda-core 0.4.0, wheels for the `free-threaded interpreter`_ are shipped to PyPI.
+
+1. Support for these builds is best effort, due to heavy use of `built-in
+   modules that are known to be thread-unsafe`_, such as ``ctypes``.
+2. For now, you are responsible for making sure that calls into ``cuda-core``
+   libraries are thread-safe. This is subject to change.
+
+.. _built-in modules that are known to be thread-unsafe: https://github.com/python/cpython/issues/116738
+.. _free-threaded interpreter: https://docs.python.org/3/howto/free-threading-python.html
+
 Installing from Conda (conda-forge)
 -----------------------------------