[FAB-13777] Fix private data base64 instructions
[FAB-13777] Fix private data base64 instructions

Document how to base64 encode in private data tutorial.

Change-Id: I0dc89fc18afd3aa79fdcd6695a9dc8139b689f6c
Signed-off-by: David Enyeart <3d699cfec69cc11a9ba1c3a1aef3260ab163489b@us.ibm.com>

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