docs: cleanup install docs

This does a few things to the home page and all-in-one single
machine install guide:

* Uses code blocks for formatting
* Adds the customary "$" to the console blocks in the
  all-in-one single machine install guide
* Instructs to use "sudo su stack" and adds a note about
  "sudo visudo" in the all-in-one single machine doc
* Creates a symbolic link to the sample local.conf and links to
  it from the install guide (note that local.conf might be old
  by now)
* Fixes the .gitignore file to only ignore local.conf in the root
  of the repository, otherwise it would ignore local.conf everywhere
  including the samples and doc/source/assets directories.

Change-Id: I50ae7bd32c4c1caa2ac8551fc54b31dd2dfae568
diff --git a/doc/source/index.rst b/doc/source/index.rst
index fcf1e82..6c42a5b 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -55,14 +55,14 @@
 
 You can quickly create a separate `stack` user to run DevStack with
 
-::
+.. code-block:: console
 
    $ sudo useradd -s /bin/bash -d /opt/stack -m stack
 
 Since this user will be making many changes to your system, it should
 have sudo privileges:
 
-::
+.. code-block:: console
 
     $ echo "stack ALL=(ALL) NOPASSWD: ALL" | sudo tee /etc/sudoers.d/stack
     $ sudo su - stack
@@ -70,7 +70,7 @@
 Download DevStack
 -----------------
 
-::
+.. code-block:: console
 
    $ git clone https://git.openstack.org/openstack-dev/devstack
    $ cd devstack
@@ -83,7 +83,8 @@
 
 Create a ``local.conf`` file with 4 passwords preset at the root of the
 devstack git repo.
-::
+
+.. code-block:: ini
 
    [[local|localrc]]
    ADMIN_PASSWORD=secret
@@ -93,12 +94,15 @@
 
 This is the minimum required config to get started with DevStack.
 
+.. note:: There is a sample :download:`local.conf </assets/local.conf>` file
+    under the *samples* directory in the devstack repository.
+
 Start the install
 -----------------
 
-::
+.. code-block:: console
 
-   ./stack.sh
+   $ ./stack.sh
 
 This will take a 15 - 20 minutes, largely depending on the speed of
 your internet connection. Many git trees and packages will be