Add note about glibc in install doc

doc/install.rst

@@ -27,6 +27,26 @@ Pre-built binary wheels are uploaded to PyPI (Python Package Index) for each rel
 You might need to run the command with ``--user`` flag or use ``virtualenv`` if you run
 into permission errors.
 
+.. note:: Parts of the Python package now require glibc 2.28+
+
+  Starting from 2.1.0, XGBoost Python package will be distributed in two variants:
+
+  * ``manylinux_2_28``: for recent Linux distros with glibc 2.28 or newer. This variant comes with all features enabled.
+  * ``manylinux2014``: for old Linux distros with glibc older than 2.28. This variant does not support GPU algorithms or federated learning.
+
+  The ``pip`` package manager will automatically choose the correct variant depending on your system.
+
+  Starting from **May 31, 2025**, we will stop distributing the ``manylinux2014`` variant and exclusively
+  distribute the ``manylinux_2_28`` variant. We made this decision so that our CI/CD pipeline won't have
+  depend on software components that reached end-of-life (such as CentOS 7). We strongly encourage
+  everyone to migrate to recent Linux distros in order to use future versions of XGBoost.
+
+  Note. If you want to use GPU algorithms or federated learning on an older Linux distro, you have
+  two alternatives:
+
+  1. Upgrade to a recent Linux distro with glibc 2.28+.  OR
+  2. Build XGBoost from the source.
+
 .. note:: Windows users need to install Visual C++ Redistributable
 
   XGBoost requires DLLs from `Visual C++ Redistributable