Added missing `bundle install` instructions.

I'm walking through the instructions and noticed that rake will not run unless a `bundle install` is performed so I added it to the instructions.
Update documentation

* Change recommendation for install path to /var/www/discourse
* Fix instructions for redis-server installation
* Set yourself as system user during install
* Clarify some instructions
Add GNU screen configuration file for vagrant love
Merge pull request #1306 from Supermathie/sysadmin-docs

Update documentation
Merge pull request #1307 from Supermathie/vagrant-screen

Add GNU screen configuration file for vagrant love
Added a missing "#" to href for TOS.
Merge pull request #1308 from happycollision/patch-1

Added a missing "#" to href for TOS.
Merge pull request #1303 from djensen47/patch-1

Added missing `bundle install` instructions.
Private message emails now include the history
create thumbnails by defaults

changed "create_thumbnails" default value to `true`
FIX: IE9 regression
Merge pull request #1310 from ZogStriP/patch-1

create thumbnails by defaults
Blocked Emails list in admin
Add a way to view staff action logs in admin
Add index to blocked_emails for last_match_at
Oops, forgot to use i18n in some places
Trust level change logs the target_user_id
Send context of where a user was deleted as a spammer so it can be logged
Tweaks to staff action logs page
Version bump to v0.9.6