Clarify -c and -q flag description

[ashley]

Changing the description of -c to Number of workers to run concurrently... and -q to in queries per worker per second..... This will clarify that the c flag is used to define the number of threads and -q is actually the number of requests per worker per second.

Motivated by #140 #143 and #158

Use Cases:

• Someone who uses the duration (-z) flag, and want to set the total number of queries per second:
  • Recognize that QPS (queries per second) is -c times -q
• Someone who wants to send 2,000 total number of queries without changing -n:
  • Recognize that -c is not the total number of requests and would set -c as 10 because the default -n is 200 so 200 * 10 = 2,000 queries

This makes more sense as a first impression, but I'm open to any recommendations!

[rakyll]

Thanks so much!!!

[ashley]

I realized that the README.md should also be updated 😃

[rakyll]

Would you be interested in sending a follow up PR to update the README?

[ashley]

@rakyll Opened #191 for review