Code review comment for lp:~hrvojem/percona-server/rn-5.5.37-35.0-5.6

- Explain what query optimiser support for the clustering keys means: the query optimiser will avoid primary clustered index reads and replace them by secondary clustered index reads in certain scenarios.
- Before the full supported syntax, add a few basic examples of CREATE TABLE etc.
- It would be very nice to have an example with a differing query plan for the same query with regular and with clustering secondary key. Might be possible to ask Tokutek for what would be a flagship example, or maybe there is an example in their docs.