Add changelog for my datasets

docs/CHANGELOG.md

@@ -12,6 +12,19 @@ For more information about `AlexsLemonade/scpca-nf` versions, please see [the re
 <!-- PUT THE NEW CHANGELOG ENTRY RIGHT BELOW THIS -->
 <!-------------------------------------------------->
 
+## TODO: Add release date for datasets
+
+* Data on the Portal can now be downloaded in three different ways: 
+  * By selecting a {ref}`single project<download_files:project downloads>` to download.
+  * By creating a {ref}`custom dataset<download_files:custom datasets>` with a selection of projects and/or samples. 
+  Custom datasets are referred to as `My Dataset` on the Portal. 
+  * By choosing one of the {ref}`Portal-wide download options<download_files:portal-wide downloads>`. 
+* Although the content of the data included in each download has not changed, the download file structures have changed. 
+See the {ref}`Downloadable Files page for more information<download_files:downloadable files>`.
+* A new section of the documentation describing possible {ref}`download options<download_options:download options>` has been added.
+* The previously named `single_cell_metadata.tsv` files that are included with each download have been renamed to `single-cell_metadata.tsv`.
+
+
 ## 2025.12.04
 
 All data on the Portal has been updated to include a number of new features.