Edit code samples in README.rst

Edit both of the code samples in the root readme file. The first code sample
incorrectly stated that Pulp Smash can be installed with `pip install
pulp_smash`, but the actual package name is `pulp-smash`. The second code sample
neglected to explain that source code must be present in order to locally
generate documentation.

README.rst

@@ -7,7 +7,7 @@ Pulp Smash
 Pulp Smash is a test suite for `Pulp`_. It lets you execute a workflow like
 this::
 
-    pip install pulp_smash
+    pip install pulp-smash
     python -m pulp_smash  # follow the instructions
 
 Pulp Smash is a GPL-licensed Python library, but no knowledge of Python is
@@ -22,5 +22,8 @@ the prompts.
 The `full documentation <http://pulp-smash.readthedocs.org/en/latest/>`_ is
 available on ReadTheDocs. It can also be generated locally::
 
+    virtualenv env && source env/bin/activate
+    git clone https://github.com/PulpQE/pulp-smash.git
+    cd pulp-smash
     pip install -r requirements.txt -r requirements-dev.txt
     make docs-html