Update Jira upgrade notes

Jira Software 7.12.x upgrade notes mentioned:

Upgrading from earlier versions?

...

• Earlier than 7.0 
  Consult the Migration hub. The Jira 7.0 release introduced significant changes. You must first upgrade to Jira 7.0 before upgrading to later versions.

Skipping major versions when upgrading Jira applications mentioned:

Jira Software specific notes
If you plan to upgrade from Jira and Jira Agile less than 6.4.x and 6.3.5 respectively, you must upgrade to Jira Software 7.0 before upgrading to Jira Software 7.1.

However, it would be great to instruct users to specifically upgrade to Jira 7.0.11 (the last release of 7.0) to avoid users running into known issues within the release versions of 7.0.x.

Other alternative would be to include small note about the known issues so users would just skip the affected version releases.

For example, a user in GHS-135977, was in the process of upgrading to Jira 7.0.0 (as the intermediate version), and he ran into the bug JRASERVER-47267 which affected Oracle users and users coming from Jira 6.4.8 or later.