Update CHANGELOG_DEV.md

Author: le1nux

CHANGELOG_DEV.md

@@ -65,3 +65,23 @@ This [PR](https://github.com/Modalities/modalities/pull/236) removes all code re
 
 **Breaking changes:** 
 * None
+* 
+
+## PR #254 Warmstart infrastructure switch
+
+This PR mainly addresses the warmstart of model training, e.g., after GPU crashes.
+
+**General Changes**
+* Fixes issue #242 
+* Warmstarts with changing infrastructure (e.g.,. different number of GPUs) are now supported.
+* Restructures the settings part of the configs to 
+* Adds various checks for consistency of model training (e.g., target tokens and number of dataset tokens mismatch)
+* Refactors all configs to be runnable again
+* Adds an interactive jupyter notebook-based Tutorial on how to use Modalities. (merged from PR #239 )
+* Adds a warmstart tutorial
+* TrainingReportGenerator that creates a report on the training setup and prints out warnings in case of inconsistencies.
+* Activation Checkpointing is now a component
+* Added further NumberConversion routines
+
+**Breaking Changes**
+* the settings part of the configs have been completely refactored