Added corosync.conf settings minimal explanation. Explain corosync-cfgtool purpose.
drbd-setup: Added DRBD configuration settings explanation
ha-system-management: Chapter description was improved
improvements: Chapter description was improved
drbd-setup: Minor TYPOs
operating-system-installation: Make clear the performance tuning guidelines reference
pacemaker-setup: Added stonith reference to Fencing subsection
Structure of the document section was improved