Make it clear that maxcpus=auto is at build time, not execution time

ChangeLog

@@ -73,8 +73,8 @@ Small changes:
     - starpu_sched_ctx_get_sched_policy_init() to starpu_sched_ctx_get_sched_policy_callback()
     as the callback function may not only be used for init purposes
   - Change the default value for configure option --enable-maxcpus to
-    auto. it allows StarPU to automatically detect the number of CPUs
-    on the running machine.
+    auto. it allows StarPU to automatically use the number of CPUs
+    on the build machine.
 
 StarPU 1.3.8
 ====================================================================

doc/doxygen/chapters/510_configure_options.doxy

@@ -184,9 +184,9 @@ Use at most <c>count</c> CPU cores.  This information is then
 available as the macro ::STARPU_MAXCPUS.
 
 The default value is <c>auto</c>. it allows StarPU to automatically
-detect the number of CPUs on the running machine. This should not be
-used if the running host has a different number of CPUs from the
-compilation node.
+detect the number of CPUs on the build machine. This should not be
+used if the running host has a larger number of CPUs than the
+build machine.
 </dd>
 
 <dt>--enable-maxnumanodes=<c>count</c></dt>