iallocator.rst: give pointers for alloc_policy semantics
iallocator.rst: give pointers for alloc_policy semantics

Signed-off-by: Adeodato Simo <16293852a0900193fe70fa7d24f714f37ba99a56@google.com>
Reviewed-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>

dimara/ganeti,andir/ganeti,leshchevds/ganeti,bitemyapp/ganeti,ganeti-github-testing/ganeti-test-1,leshchevds/ganeti,mbakke/ganeti,onponomarev/ganeti,yiannist/ganeti,ganeti/ganeti,ganeti/ganeti,yiannist/ganeti,apyrgio/snf-ganeti,apyrgio/ganeti,ganeti/ganeti,mbakke/ganeti,mbakke/ganeti,grnet/snf-ganeti,onponomarev/ganeti,dimara/ganeti,bitemyapp/ganeti,apyrgio/ganeti,andir/ganeti,apyrgio/snf-ganeti,andir/ganeti,yiannist/ganeti,ganeti-github-testing/ganeti-test-1,grnet/snf-ganeti,leshchevds/ganeti