This ticket pertains to the Getting Started guide on the apache mesos website
The current instructions for installing on Mac OS X only include instructions for Yosemite. The instructions to build for El Capitan are identical except in the case of upgrading from Yosemite to El Capitan. To build after an upgrade requires a trivial (but important) step which is non-obvious – you have to rerun 'xcode-select --install' after you complete the upgrade.
Let's change the heading for installing on Mac OS X to say:
Mac OS X Yosemite & El Capitan
and then add a comment at the bottom of the section to point out that a rerun of 'xcode-select --install' is necessary after an upgrade from Yosemite to El Capitan.