Switch links to jmeter to https and mention Building and contributing doc
Switch links to jmeter to https and mention Building and contributing doc

git-svn-id: https://svn.apache.org/repos/asf/jmeter/trunk@1813339 13f79535-47bb-0310-9956-ffa450edef68

Former-commit-id: 5c934bb8fd00dc84f45fcea531e62f3596887e84
apache/jmeter,etnetera/jmeter,ham1/jmeter,ham1/jmeter,ham1/jmeter,etnetera/jmeter,benbenw/jmeter,apache/jmeter,ham1/jmeter,benbenw/jmeter,benbenw/jmeter,benbenw/jmeter,apache/jmeter,ham1/jmeter,apache/jmeter,etnetera/jmeter,etnetera/jmeter,etnetera/jmeter,apache/jmeter