still need to test row merge

multi-node/col-split/README.md

@@ -1,14 +1,14 @@
-Column Split Version of XGBoost
+Distributed XGBoost: Column Split Version
 ====
 * run ```bash run-mushroom.sh```
 
-Steps to use column split version
+How to Use
 ====
 * First split the data by column, 
 * In the config, specify data file as containing a wildcard %d, where %d is the rank of the node, each node will load their part of data
 * Enable column split mode by ```dsplit=col```
 
-Note on the Column Split Version
+Notes
 ====
 * The code is multi-threaded, so you want to run one xgboost-mpi per node
 * The code will work correctly as long as union of each column subset is all the columns we are interested in.