DOC: Update AnnotationFileFormat.md to list "0.2.1 (2022-03-04)" version

This commit explicitly list version introduced in 6ca9f71 (ENH: Add structure
ID to JSON format) and 5cedbdf (ENH: Support structure ID in file format
converter. ) through PR BICCN#209

Documentation/developer_guide/AnnotationFileFormat.md

@@ -14,7 +14,7 @@ _The latest version listed below should correspond to the version hard-coded in
 
 [home-py]: https://github.com/BICCN/cell-locator/blob/master/Modules/Scripted/Home/Home.py
 
-## Next Release
+## 0.2.1 (2022-03-04)
 
 Add the `structure` object to control point. `null` for values with missing structure (outside of atlas, converted from old file, etc.)