Added api-paste.ini info to trove install chapter

The juno rhel/centos/fedora packages are missing the
required api-paste.ini file.

This patch describes how to get the file and tell
trove how to use it.

Change-Id: I6649ffadd0e4cac683329b03e1b8bb3cb61c54c8
Closes-Bug: #1384147
Merge "Added api-paste.ini info to trove install chapter" into stable/juno