Improve intro to the exit codes topic
Improve intro to the exit codes topic

Summary:
- Buck sometimes reports `FATAL_GENERIC` when it isn't able to detect what went wrong.
- Reference the term *binary protocol* so that search engines index the page under that term. Some people use "binary protocol" to refer to a program's set of exit codes.

Reviewed By: sbalabanov

fbshipit-source-id: 1b929f5ceb

zpao/buck,romanoid/buck,nguyentruongtho/buck,Addepar/buck,SeleniumHQ/buck,facebook/buck,rmaz/buck,kageiit/buck,romanoid/buck,SeleniumHQ/buck,SeleniumHQ/buck,SeleniumHQ/buck,zpao/buck,rmaz/buck,SeleniumHQ/buck,romanoid/buck,romanoid/buck,romanoid/buck,kageiit/buck,romanoid/buck,JoelMarcey/buck,nguyentruongtho/buck,brettwooldridge/buck,brettwooldridge/buck,SeleniumHQ/buck,brettwooldridge/buck,rmaz/buck,romanoid/buck,JoelMarcey/buck,Addepar/buck,brettwooldridge/buck,JoelMarcey/buck,JoelMarcey/buck,brettwooldridge/buck,rmaz/buck,JoelMarcey/buck,SeleniumHQ/buck,JoelMarcey/buck,romanoid/buck,brettwooldridge/buck,zpao/buck,kageiit/buck,romanoid/buck,SeleniumHQ/buck,rmaz/buck,brettwooldridge/buck,nguyentruongtho/buck,rmaz/buck,rmaz/buck,JoelMarcey/buck,nguyentruongtho/buck,rmaz/buck,facebook/buck,facebook/buck,facebook/buck,rmaz/buck,brettwooldridge/buck,zpao/buck,Addepar/buck,SeleniumHQ/buck,rmaz/buck,JoelMarcey/buck,zpao/buck,JoelMarcey/buck,Addepar/buck,Addepar/buck,Addepar/buck,zpao/buck,rmaz/buck,Addepar/buck,JoelMarcey/buck,nguyentruongtho/buck,nguyentruongtho/buck,SeleniumHQ/buck,nguyentruongtho/buck,Addepar/buck,JoelMarcey/buck,romanoid/buck,kageiit/buck,Addepar/buck,brettwooldridge/buck,SeleniumHQ/buck,romanoid/buck,kageiit/buck,romanoid/buck,facebook/buck,romanoid/buck,brettwooldridge/buck,Addepar/buck,SeleniumHQ/buck,Addepar/buck,kageiit/buck,JoelMarcey/buck,brettwooldridge/buck,rmaz/buck,Addepar/buck,zpao/buck,JoelMarcey/buck,rmaz/buck,facebook/buck,Addepar/buck,facebook/buck,SeleniumHQ/buck,brettwooldridge/buck,brettwooldridge/buck,kageiit/buck