Amend gem description

The tool is configurable--let's emphasize that.

Change-Id: Iad3e2dfc483a71ce381d08e4b475fba8f77692bc
Reviewed-on: http://gerrit.causes.com/44726
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>