updated the README and installation instructions in the docs to mention that setting the PYTHONPATH is only necessary if using pyro as a python module

Author: harpolea

README.md

@@ -70,7 +70,9 @@ https://pyro2.readthedocs.io/
   - The remaining steps are:
 
       * Set the `PYTHONPATH` environment variable to point to the `pyro2/`
-        directory.
+        directory (note this is only needed if you wish to use pyro as a python
+        module - this step is not necessary if you only run pyro via the
+        commandline using the `pyro.py` script).
 
       * Define the environment variable `PYRO_HOME` to point to the
         `pyro2/` directory (only needed for regression testing)

docs/source/installation.rst

@@ -18,15 +18,18 @@ The following python packages are required:
 
 The following steps are needed before running pyro:
 
-* add ``pyro/`` to your ``PYTHONPATH`` environment variable.  For
+* add ``pyro/`` to your ``PYTHONPATH`` environment variable (note this is only
+needed if you wish to use pyro as a python
+module - this step is not necessary if you only run pyro via the
+commandline using the `pyro.py` script).  For
   the bash shell, this is done as:
 
     .. code-block:: none
 
        export PYTHONPATH="/path/to/pyro/:${PYTHONPATH}"
 
 * define the environment variable ``PYRO_HOME`` to point to
-  the ``pyro2/`` directory
+  the ``pyro2/`` directory (only needed for regression testing)
 
     .. code-block:: none