Update doc --mergeunknown for after 35b19de
For the expectations 'FAIL' means the same than 'TEXT', 'IMAGE+TEXT' or 'AUDIO'

  * We should mark the test as green also when the result is one of
    'TEXT' 'IMAGE+TEXT' or 'AUDIO', and 'FAIL' is on the expectation

  * This is defined on:
    $WebKit/Tools/Scripts/webkitpy/layout_tests/models/test_expectations.py
Paint red if any actual result is not in the expected
Remove green color for no error.
--ignoreunknown merges also noerror with --mergeunknown
Pushed results up to r167756