Update install.md

Author: tturocy

content/install.md

@@ -2,6 +2,14 @@
 title: Install Gambit
 ---
 
+## Gambit 16.4
+
+**Gambit 16.4.0** was released n **2025-09-05**.
+
+* [Download](https://github.com/gambitproject/gambit/releases/tag/v16.4.0)
+* [Documentation](https://gambitproject.readthedocs.io/en/v16.4.0)
+* [PyGambit on PyPI](https://pypi.org/project/pygambit/16.4.0)
+  
 ## Gambit 16.3
 
 **Gambit 16.3.1** was released n **2025-08-18**.