NMS-6641: Documentation CiscoIpSlaMonitor

- Migrate pull request to OpenNMS devel instead development/docs

JIRA: http://issues.opennms.org/browse/NMS-6641
- Migrated from wiki http://www.opennms.org/wiki/Cisco_IP_SLA_Monitor

Todo Review:
- [x] Typo and grammar
- [x] Formatting and conventions
- [x] Content