devstack: Adding a README for ironic-bm-logs directory
devstack: Adding a README for ironic-bm-logs directory

Adding a README file to be put into the ironic-bm-logs/ directory that
explains the virtual bare-metal log files.

Change-Id: If4fc6b53273d39c65db0251957795d214440118d

pshchelo/ironic,pshchelo/ironic,NaohiroTamura/ironic,SauloAislan/ironic,openstack/ironic,NaohiroTamura/ironic,openstack/ironic,SauloAislan/ironic