Improvements for README.md

Simple improvements to avoid some trip ups and save a few minutes of troubleshooting. The guide is quite long and it's easy to get into a habit of copy and pasting.

Adding a init.d script without unicorn or puma, just sidekiq

CentOS Install - PUIAS repo

Update Centos 6.4 guide to obtain git via RPM instead of compilation

fix typo

Tell users to ignore the complain that the init script is not up-to-date.

Add mod_headers module dependency for RequestHeader directive

Update README.md

add tips to solve two errors:

$git push -u origin master
Access denied.
fatal: Could not read from remote repository.

and:

$ git push -u origin master
/usr/local/lib/ruby/2.0.0/net/http.rb:918:in `connect': SSL_connect returned=1 errno=0 state=SSLv3 read server certificate B: certificate verify failed (OpenSSL::SSL::SSLError)
	from /usr/local/lib/ruby/2.0.0/net/http.rb:918:in `block in connect'
	from /usr/local/lib/ruby/2.0.0/timeout.rb:52:in `timeout'
	from /usr/local/lib/ruby/2.0.0/net/http.rb:918:in `connect'
	from /usr/local/lib/ruby/2.0.0/net/http.rb:862:in `do_start'
	from /usr/local/lib/ruby/2.0.0/net/http.rb:851:in `start'
	from /home/git/gitlab-shell/lib/gitlab_net.rb:62:in `get'
	from /home/git/gitlab-shell/lib/gitlab_net.rb:17:in `allowed?'
	from /home/git/gitlab-shell/lib/gitlab_shell.rb:60:in `validate_access'
	from /home/git/gitlab-shell/lib/gitlab_shell.rb:24:in `exec'
	from /home/git/gitlab-shell/bin/gitlab-shell:16:in `<main>'
fatal: Could not read from remote repository.

Incorporate fix for incorrect http redirect

Incorporates fix from https://github.com/gitlabhq/gitlabhq/issues/715 to make gitlab properly redirect to https instead of http when configured for https

Added instructions for the implementation of an SSL certificate

Add github import script

Changing gitlab-shell version from 1.7.0 to 1.7.4

gitllab 6.2 needed gitlab-shell version >= 1.7.4

Change branch name 6-0-stable to 6-2-stable

Because the latest version of init script is not compatible with the version 6.0

Apache config - better based on SSL config

This is a better proxy config which is based on the
gitlab-ssl.conf.

Update init.d for CentOS 6.4 and GitLab 6.2

Update service files for use with Gitlab 6.2

Set RAILS_ENV via variable.
Also includes changes from PR #138 and #145.

Fix certificate error when wget fetches EPEL gpg key

Update centos install guide with postgresql details