docs: Updated permissions. Tweaked install details

Added nginx to installation packages. We say that our install uses
nginx, so users should skip nginx if they want to use apache. Also,
our group permissions depend on a web server being installed.

Changed install directory for mediagoblin acct to /var/lib/mediagoblin
It works better if we need to back up data.

Assigned mediagoblin user to the same group as the web server. This
is needed so that the server can access uploaded media.

Created mediagoblin group for non-web-server things such as logs.

docs/source/siteadmin/deploying.rst

@@ -69,14 +69,15 @@ On a DEB-based system (e.g Debian, gNewSense, Trisquel, Ubuntu, and
 derivatives) issue the following command::
 
     sudo apt-get install git-core python python-dev python-lxml \
-        python-imaging python-virtualenv npm nodejs-legacy automake
+        python-imaging python-virtualenv npm nodejs-legacy automake \
+        nginx
 
 On a RPM-based system (e.g. Fedora, RedHat, and derivatives) issue the
 following command::
 
     sudo yum install python-paste-deploy python-paste-script \
         git-core python python-devel python-lxml python-imaging \
-        python-virtualenv npm automake
+        python-virtualenv npm automake nginx
 
 Configure PostgreSQL
 ~~~~~~~~~~~~~~~~~~~~
@@ -159,10 +160,25 @@ helps to keep it more secure.
 
 The following command (entered as root or with sudo) will create a
 system account with a username of ``mediagoblin``. You may choose a different
-username if you wish.::
+username if you wish.
 
-    sudo useradd -c "GNU MediaGoblin system account" -d /home/mediagoblin -U -m -r mediagoblin
+If you are using a Debian-based system, enter this command::
 
+    sudo useradd -c "GNU MediaGoblin system account" -d /var/lib/mediagoblin -m -r -g www-data mediagoblin
+
+If you are using an RPM-based system, enter this command::
+
+    sudo useradd -c "GNU MediaGoblin system account" -d /var/lib/mediagoblin -m -r -g nginx mediagoblin
+
+This will create a ``mediagoblin`` user and assign it to a group that is
+associated with the web server. This will ensure that the web server can
+read the media files (images, videos, etc.) that users upload.
+
+We will also create a ``mediagoblin`` group and associate the mediagoblin
+user with that group, as well::
+  
+    sudo groupadd mediagoblin && sudo usermod --append -G mediagoblin mediagoblin
+       
 No password will be assigned to this account, and you will not be able
 to log in as this user. To switch to this account, enter::
 
@@ -185,10 +201,14 @@ Setting up the working directory requires that we first create the directory
 with elevated priviledges, and then assign ownership of the directory
 to the unpriviledged system account.
 
-To do this, enter either of the following commands, changing the defaults
+To do this, enter the following command, changing the defaults to suit your
-to suit your particular requirements::
+particular requirements. On a Debian-based platform you will enter this::
 
-    sudo mkdir -p /srv/mediagoblin.example.org && sudo chown -hR mediagoblin: /srv/mediagoblin.example.org
+    sudo mkdir -p /srv/mediagoblin.example.org && sudo chown -hR mediagoblin:www-data /srv/mediagoblin.example.org
+
+On an RPM-based distribution, enter this command::
+
+    sudo mkdir -p /srv/mediagoblin.example.org && sudo chown -hR mediagoblin:nginx /srv/mediagoblin.example.org
 
 .. note::
 
@@ -349,14 +369,12 @@ one of the following commands.
 On a DEB-based system (e.g Debian, gNewSense, Trisquel, Ubuntu, and
 derivatives) issue the following commands::
 
-    sudo apt-get install nginx
     sudo ln -s /srv/mediagoblin.example.org/nginx.conf /etc/nginx/sites-enabled/
     sudo systemctl enable nginx
 
 On a RPM-based system (e.g. Fedora, RedHat, and derivatives) issue the
 following commands::
 
-    sudo yum install nginx
     sudo ln -s /srv/mediagoblin.example.org/nginx.conf /etc/nginx/conf.d/
     sudo systemctl enable nginx