Vendors Compete.

Summary:
Encourage various vendors to publish their RocksDB benchmark.
This will be a central repositiry that will have links to
vendor-published benchmark results.

Test Plan: none.

Reviewers: xjin, haobo, igor, sdong, jamesgpearce

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16677