CHANGELOG: add a note about _fromstream() and _fromstream_commit()

CHANGELOG.md

@@ -8,6 +8,11 @@ v0.24 + 1
 * `git_commit_create_buffer()` creates a commit and writes it into a
   user-provided buffer instead of writing it into the object db.
 
+* `git_blob_create_fromstream()` and
+  `git_blob_create_fromstream_commit()` allow you to create a blob by
+  writing into a stream. Useful when you do not know the final size or
+  want to copy the contents from another stream.
+
 ### API removals
 
 ### Breaking API changes