Update affinity README.

README.affinity

@@ -14,15 +14,7 @@ shepherds are allocated. It is implemented as a colon-seperated list of
 cpustrings, where each cpustring is a shepherd. It is controlled by the
 environment variable QT_CPUBIND. See src/affinity/README.binders for more details.
 
-Failing that, other APIs are also supported, but since they provide less
-information, they're used primarily for querying the number of cores and
-pinning worker threads to them in a round-robin fashion (libnuma also supports
-pinning memory).
-
-Unless such an affinity library is available, worker threads are NOT pinned,
-especially on Linux. Unfortunately, the usual sched_setaffinity() function that
-Linux provides is not portable, and the differences in arguments across
-different versions of Linux are difficult to detect.
+Unless hwloc is available, worker threads are NOT pinned.
 
 There are several environment variables that can be used to control CPU
 affinity and parallelism. See the qthread_initialize() man page for details.