docs: Update getting started documentation

Currently the getting started documentation is somewhat incorrect:
usage of pip3 install is not necessary as "regular" usage of
pegleg entails using ./tools/pegleg.sh which uses the Pegleg
Docker image.

Also, the CLI guide doesn't include any useful examples so some
have been added.

Change-Id: I851b1c8b4f9c38672fce7b4a017e31882c7006ea
Depends-On: Iaa928ec2f777ed6f899d3b1790f5f9de613da9bb

doc/source/cli.rst

@@ -19,7 +19,15 @@ Pegleg CLI
 ==========
 
 The Pegleg CLI is used in conjunction with the script located in pegleg/tools
-called pegleg.sh.
+called ``pegleg.sh``.
+
+.. note::
+
+  The default workspace for the ``pegleg.sh`` script is ``/workspace``. The
+  examples below require that this workspace be used.
+
+Environment Variables
+=====================
 
 ::
 
@@ -33,6 +41,9 @@ called pegleg.sh.
 
         Example: $IMAGE=quay.io/attcomdev/pegleg:latest
 
+Usage
+=====
+
 To run:
 
 .. code-block:: console
@@ -41,6 +52,25 @@ To run:
     export IMAGE=<docker_image>
     ./pegleg.sh <command> <options>
 
+For example:
+
+.. code-block:: console
+
+  cd /opt/airship-pegleg
+  export WORKSPACE=/opt/airship-treasuremap
+  ./tools/pegleg.sh site -r /workspace --help
+
+.. note::
+
+  If ``sudo`` permissions are required to execute ``pegleg.sh``, then it is
+  necessary to use the ``-E`` flag with ``sudo`` in order for the current
+  environment to be used. For example:
+
+  .. code-block:: console
+
+    cd /opt/airship-pegleg
+    export WORKSPACE=/opt/airship-treasuremap
+    sudo -E ./tools/pegleg.sh site -r /workspace --help
 
 CLI Options
 ===========

doc/source/getting_started.rst

@@ -40,11 +40,7 @@ Before using Pegleg, you must:
 
     git clone https://git.airshipit.org/airship-pegleg
 
-2. Install the required packages in airship-pegleg/src/bin/pegleg:
-
-.. code-block:: console
-
-     pip3 install -r airship-pegleg/src/bin/pegleg/requirements.txt -r airship-pegleg/src/bin/pegleg/test-requirements.txt
+2. Install `Docker CE`_, as Pegleg relies on it for CLI execution.
 
 3. Clone the repos containing your `site definition libraries`_ into the
 local filesystem where Pegleg is running, as Pegleg can only work with files
@@ -54,6 +50,6 @@ You will then be able to use all of Pegleg's features through the CLI. See CLI_
 information.
 
 .. _Document Fundamentals: https://airship-pegleg.readthedocs.io/en/latest/authoring_strategy.html
-.. _CLI: https://airship-pegleg.readthedocs.io/en/latest/cli.html
-.. _Deckhand: https://airship-deckhand.readthedocs.io/en/latest/
+.. _Docker CE: https://docs.docker.com/install/
 .. _site definition libraries: https://airship-pegleg.readthedocs.io/en/latest/artifacts.html#definition-library-layout
+.. _CLI: https://airship-pegleg.readthedocs.io/en/latest/cli.html