Add screenshot to README
Add screenshot to README

git-svn-id: https://svn.apache.org/repos/asf/jmeter/trunk@1821794 13f79535-47bb-0310-9956-ffa450edef68

Former-commit-id: 63aa01629c2acb0c249965d4e87763ca8596128b
etnetera/jmeter,apache/jmeter,benbenw/jmeter,etnetera/jmeter,etnetera/jmeter,benbenw/jmeter,apache/jmeter,apache/jmeter,ham1/jmeter,benbenw/jmeter,apache/jmeter,ham1/jmeter,ham1/jmeter,etnetera/jmeter,etnetera/jmeter,apache/jmeter,ham1/jmeter,benbenw/jmeter,ham1/jmeter