Updating linux build docs

Include some small text that clarifies how to run overviewer after a `build` step

docs/building.rst

@@ -133,6 +133,8 @@ You will need the following packages (at least):
 Then to build::
 
     python setup.py build
+    
+At this point, you can run ``./overviewer.py`` from the current directory, so to run it you'll have to be in this directory and run ``./overviewer.py`` or provide the the full path to ``overviewer.py``.  Another option would be to add this directory to your ``$PATH``.   Note that there is a ``python setup.py install`` step that you can run which will install things into ``/usr/local/bin``, but this is not recommended as it might conflict with other installs of Overviewer
 
 OSX
 ---