Update changelog with loal indexing removal

CHANGELOG.md

@@ -21,6 +21,9 @@ SNIRF uses the [Semantic Versioning](https://semver.org) scheme.
 * Specified that `aux{i}/dataTimeSeris` is a 2D array. Multiple channels of data can be present, otherwise 2nd dimension should be 1.
 * Added language preventing `metaDataTags` sub-groups
 * Added notice that the summary table is intended to be machine-readable
+* Removed local channel indexing owing to incomplete specification.
+
+The implementation did not define a mapping from local to global indices, and was thus incomplete.
 
 ### `v1.0` (September 23 2021)