Add best practice to book for loading row key only
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Key: HBASE-3768
URL: https://issues.apache.org/jira/browse/HBASE-3768
Project: HBase
Issue Type: Improvement
Reporter: Erik Onnen
Priority: Minor
Book and wiki FAQs are missing guidance on the recommended practice for loading
row keys only during a scan.
Patch attached based on jdcryans' feedback from IRC.
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