Update CHANGELOG.md
Update CHANGELOG.md

Update CHANGELOG.md to indicate that the changelog is now maintained in GitHub.

Signed-off-by: David Enyeart <3d699cfec69cc11a9ba1c3a1aef3260ab163489b@us.ibm.com>

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