some more notes

1 files changed, 2 insertions, 1 deletions

diff --git a/README.md b/README.md
index 9674d90..a0ca5b9 100644
--- a/README.md
+++ b/README.md
@@ -249,7 +249,8 @@ e.g.
 
 The mapper function gets from HBaseRawSource a tuple containing two fields: (rowkey, row).   
 The first field is the row key, the second is the row Result object. You can then process the row as needed.   
-The sink will write the output fields as columns under the provided family and field name as the column name.   
+The sink expects a rowkey field in the tuple it gets to use as a row key (it doesn't have to be the same as the one emitted by the source)).
+It will then write the output fields (except the rowkey) as columns under the provided family and field name as the column name.   
 You can also provide the field name as a full qualifier (family:column) to specify a different family than was declared in the source.  
 e.g.