Fixes #8464

Also https://metabase.com/start/jar.html still mention Java 7:

> Metabase requires that you have Java **7** or higher available on your system. We have run Metabase with both the OpenJDK and Oracle JDK, so feel free to use either.

Configuring Logging Level in Operations Guide was missing a TOC entry.

Docs show the usage of VisualVM for local and remote (via JMX)
monitoring of a Metabase instance.

Since the metabase-deploy repo seems to no longer get updated, the instructions listed here won't work anymore. Unfortunately Heroku does not offer re-deployments. Adding an empty commit and pushing fixes the problem.

Adding a note about restrictions on subnets that apply to ELB and RDS, slightly more nuanced than "just check all the boxes". See http://discourse.metabase.com/t/cannot-setup-on-aws-in-vpc/2166 for more detail.

Fixing step3 to point to the correct URL which is:
https://github.com/metabase/metabase-buildpack