[ignite] fix Ignite README.md.    (#1215)
[ignite] fix Ignite README.md.    (#1215)

* clarify steps and remove specific YCSB / ignite version numbers
* closes #1213 

brianfrankcooper/YCSB,leschekhomann/YCSB,ChristianNavolskyi/YCSB,leschekhomann/YCSB,brianfrankcooper/YCSB,ChristianNavolskyi/YCSB,leschekhomann/YCSB,brianfrankcooper/YCSB,ChristianNavolskyi/YCSB,leschekhomann/YCSB,brianfrankcooper/YCSB,ChristianNavolskyi/YCSB