Add a new "Guide To Monitor" with walkthroughs of the new editor.
Updates from review of monitoring guide.
Updates to create monitor docs based on feedback.
Convert monitor guide to markdown.
More updates of monitoring guide.

- Add info about API to FAQ.
- Add info about notifying users outside of datadog.
Link to guide to monitoring in nav.
Fix typo in guide to monitoring.
Update images for monitoring guide.
Comment out process monitoring docs for now.

Will enable once 5.1.0 is out.
New image for custom monitor
Merge pull request #235 from DataDog/conor/guide-to-monitoring

Add a new "Guide To Monitor" with walkthroughs of the new editor.