Could add some explanation for each test application under app/ to README?

[xiaonan-INTC]

In order to let user know what those test applicaions mainly do(test point)?

[jovanbulck]

Thank you for opening this issue and the suggestion! Yes, I agree this is currently left unclear, so I hope to make some time next week to improve the documentation and selftest system.

Also relates to #21 where new and better example programs should be added for every SGX-Step feature..