Create ossec_alerts.md

* Copied information from install.md
* Added more detailed instructions
Formatting, refinements and additions
* Gmail instructions
* Analyzing alerts
* Add table for problem/solution
* Appropriate spacing
* Fix heading
Edits to ossec_alerts.md

* Addresses the individual comments on #807
Updates per #807

* Recommend Google 2-step verification
* Update support e-mail address
No active response, server-agent explanation
Merge pull request #807 from ageis/ossec-alert-doc

Elaborate on OSSEC alert instructions