Update storage-ref-azcopy-copy.md to clarify --dry-run functionality

'dry-run' functionality does not work as expected since it ignores '--overwrite=false'. This change makes sure users are aware of this limitation. For further details see Azure/azure-storage-azcopy#1904

Author: natedotzlaf

articles/storage/common/storage-ref-azcopy-copy.md

@@ -253,7 +253,7 @@ Copy a subset of buckets by using a wildcard symbol (*) in the bucket name from
 
 `--disable-auto-decoding`    False by default to enable automatic decoding of illegal chars on Windows. Can be set to true to disable automatic decoding.
 
-`--dry-run`    Prints the file paths that would be copied by this command. This flag doesn't copy the actual files.
+`--dry-run`    Prints the file paths that would be copied by this command. This flag doesn't copy the actual files. Does not currently honor '--overwrite' flag and when using '--overwrite=false' will list files in the source directory whether or not they exist in the destination directory.
 
 `--exclude-attributes`    (string)    (Windows only) Exclude files whose attributes match the attribute list. For example: A;S;R