Adds note about block size settings to accomodate custom block sizes

Change-Id: I6bc4c09066855d82bd5f17ba40ce1909b7443c99
Closes-bug: 1197449
devstack.org refers to Fedora 18, not 16

Change-Id: I45730a0105bad563fd3565fd92ad8ff9ca7ffbc9
Merge "devstack.org refers to Fedora 18, not 16"
Merge "Adds note about block size settings to accomodate custom block sizes"