Merge pull request #54 from norton/dev

Add support for disabling apps to build via KERL_CONFIGURE_DISABLE_APPLICATIONS
Update README.md

* Add a note on Tuning section about .kerlrc side effect
* Add an example of using shell `export` command in .kerlrc for build tuning
Merge pull request #56 from jj1bdx/jj1bdx-readme-diff

Update README.md