Document JIRA's requirement to be able to communicate with itself with it's base URL

Problem Definition

As of JIRA 7.1, JIRA needs to be able to communicate with itself in order to download resources from itself.

This is not currently documented in: https://confluence.atlassian.com/adminjiraserver071/jira-applications-installation-requirements-802592164.html or any other locations.

For a relevant background on this please see: How to fix gadget titles showing as __MSG_gadget

Suggested Solution

Provide clear instructions that JIRA needs to be able to communicate with itself through JIRA's BASE URL.

Workaround

Use the Knowledge Base Article linked for technical details relating to this problem.