https://www.ruby-lang.org/en/news/2015/04/13/ruby-2-1-6-released/

Rephrased wording in the documentation to say "installation from source" instead of  "manual installation" or similar.

closes #8718, closes #8721

ADD: Note on how to setup dns hostname resolution and why it is necessary to make the software run properly.

Similar to https://github.com/gitlabhq/gitlabhq/blob/master/doc/install/database_mysql.md clarify that `template1=#` is part of the prompt.

Add documentation changes to:

 * Set the permissions of the unix socket properly
 * Create the directory for the socket
 * Make sure tmpfiles.d persists said directory

The first change makes sure gitlabl can connect to the socket. The latter two
avoid redis from failing to start on systemd-based systems, including recent
versions of Debian.

Fixes
https://github.com/gitlabhq/gitlabhq/commit/2b35c887904b6a7a05a7c88fdf1ccd66ba943e20#commitcomment-7829537,
https://github.com/gitlabhq/gitlabhq/commit/5704e6fee9d2dea67c4a91b43d06a9958484d29b#commitcomment-7829367,
&
https://github.com/gitlabhq/gitlabhq/commit/5704e6fee9d2dea67c4a91b43d06a9958484d29b#commitcomment-7829381

This patch changes default permission of the gitlab/log directory to
u+rwX,go-w. This is done to make the directory NOT readable by group and
others and to avoid logrotate complaining about it. chmod 755 is not
used to avoid setting executable bit on file within the log dir.