Update installation.rst stating version support policy (#1665)

* Update installation.rst stating version support policy

* Update docs/installation.rst

Co-authored-by: Joe Hamman <jhamman1@gmail.com>

* Update docs/installation.rst

---------

Co-authored-by: Joe Hamman <jhamman1@gmail.com>

docs/installation.rst

@@ -6,6 +6,11 @@ Zarr depends on NumPy. It is generally best to `install NumPy
 appropriate for your operating system and Python distribution. Other dependencies should be
 installed automatically if using one of the installation methods below.
 
+Note: Zarr has endorsed `Scientific-Python SPEC 0 <https://scientific-python.org/specs/spec-0000/>`_ and now follows the version support window as outlined below: 
+
+- Python: 36 months after initial release
+- Core package dependencies (e.g. NumPy): 24 months after initial release
+
 Install Zarr from PyPI::
 
     $ pip install zarr