update kubernetes example-app explanation
update kubernetes example-app explanation

Clarify some potentially confusing issues with how to run and build the
example-app binary.

circleci/dex,coreos/dex,rithujohn191/dex,coreos/dex,chub/coreos-dex,circleci/dex,ericchiang/dex,rithujohn191/dex,rithujohn191/dex,Calpicow/dex,wolfeidau/dex,chub/coreos-dex,Calpicow/dex,coreos/dex,ericchiang/dex,chub/coreos-dex,Calpicow/dex,circleci/dex,wolfeidau/dex,wolfeidau/dex,ericchiang/dex