Update changes.txt for 1.2.5 patch

Author: WardBrian

docsrc/changes.rst

@@ -7,6 +7,13 @@ What's New
 
 For full changes, see the `Releases page <https://github.com/stan-dev/cmdstanpy/releases>`_ on GitHub.
 
+CmdStanPy 1.2.5
+---------------
+
+- Fixed issues that arose when running a model with no parameters using CmdStan 2.36.0+
+
+Reminder: The next non-bugfix release of CmdStanPy will be version 2.0, which will remove all existing deprecations.
+
 CmdStanPy 1.2.4
 ---------------