Update perfiz-config-syntax.markdown file to have enhanced/proper meaning for Load pattern types

[ZenwalkerD]

Describe the bug
The documentation for perfiz.config is not very well explained. Especially for load pattern type

Based on what i could gather from Gatlin website; i prepared the markup

* Open model keywords
  * nothingFor: Pause for a given duration.
  * atOnceUsers: Injects a given number of users at once.
  * rampUsers: Injects a given number of users distributed evenly on a time window of a given duration.
  * constantUsersPerSec: Injects users at a constant rate, defined in users per second, during a given duration. Users will be injected at regular intervals.
  * rampUsersPerSec: Injects users from starting rate to target rate, defined in users per second, during a given duration. Users will be injected at regular intervals.
  * heavisideUsers
* Closed model keywords
  * constantConcurrentUsers: Inject so that number of concurrent users in the system is constant
  * rampConcurrentUsers: Inject so that number of concurrent users in the system ramps linearly from a number to another

However; some are still missing and some are very vague and does not explains well well with lot more examples of mixing the patterns as well.

It would be great if the documentation is enhanced alot more!