Add configtx.yaml link to channel update doc
Add configtx.yaml link to channel update doc

Change-Id: I153b5b16c5cc03e21d2c4c496b5f6a7743b81316
Signed-off-by: joe-alewine <fe2d55ddcdde6f951d073228e1f2dc081e79a271@ibm.com>

hyperledger/fabric,stemlending/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,manish-sethi/fabric,manish-sethi/fabric-sidedb,jimthematrix/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,stemlending/fabric,jimthematrix/fabric,stemlending/fabric,stemlending/fabric,hyperledger/fabric