Several issue worth checking in documentation

[elgris]

1. https://docs.zmon.io/en/latest/intro.html:

• no zmon-eventlog-service on the diagram. However, it is listed in "minimum ZMON setup requirements"
• sentence "ZMON provides many custom wrappers that bind to the selected entity". There should be a link to list of wrappers. If there is no documentation about wrappers - it should be created.
• sentence "ZMON provides many custom wrappers that bind to the selected entity". Better add a screenshot illustrating the sentence.
• sentence "REST API and CLI". Missing link to REST API and CLI documentation

2. https://docs.zmon.io/en/latest/getting-started.html:

• Vagrant is deprecated, better provide a description of setting up with docker compose
• Screenshots illustrating the actions (Create a new Check, Create an Alert, etc) could be useful

3. https://docs.zmon.io/en/latest/user/entities.html

• What is entity "type" and what is it used for?

4. https://docs.zmon.io/en/latest/user/check-definitions.html

• "Using trial run" section lacks description or link to description

5. https://docs.zmon.io/en/latest/user/alert-definitions.html

• Could not find documentation that describes configuration of e-mail and SMS gateways.
• Missing link to https://docs.zmon.io/en/latest/user/notifications.html.

6. https://docs.zmon.io/en/latest/user/dashboards.html

• Need to specify somewhere at the beginning that Flot charts is used for widgets

7. https://docs.zmon.io/en/latest/user/check-commands.html

• Examples are missing for: metric_data, query_logs, count_logs, methods of history
• No information about how to configure access to AWS Cloudwatch
• It's unclear how Counter works until you read that section to the end. Better to put an explanation first. It should explain what counter is, how it's stored, how it's accessed from the checks.
• Elasticsearch. How does that piece authenticate with Elasticsearch if oauth2 parameter is false?
• "If url is None, then the plugin will use the default Elasticsearch cluster set in worker configuration.": worker configuration should be a link pointing to worker documentation
• Better to explain how oauth2_token_name (check HTTP section) works

8. https://docs.zmon.io/en/latest/installation/requirements.html

• Worth adding links to Redis, PostgreSQL and Cassandra projects