Add notes for the Process#clock_getres spec

spec/ruby/core/process/clock_getres_spec.rb

@@ -2,7 +2,10 @@ require_relative '../../spec_helper'
 require_relative 'fixtures/clocks'
 
 describe "Process.clock_getres" do
-  platform_is_not :freebsd do # clock_getres() seems incorrect on FreeBSD
+  # clock_getres() seems completely buggy on FreeBSD:
+  # https://rubyci.org/logs/rubyci.s3.amazonaws.com/freebsd11zfs/ruby-trunk/log/20190428T093003Z.fail.html.gz
+  platform_is_not :freebsd do
+    # NOTE: Look at fixtures/clocks.rb for clock and OS-specific exclusions
     ProcessSpecs.clock_constants_for_resolution_checks.each do |name, value|
       it "matches the clock in practice for Process::#{name}" do
         times = []